Magically enhancing claws
First and foremost, a necklace of natural attacks from Savage Species allows you to enhance your claws as magic weapons, including with special weapon properties. This is absolutely critical if the weretiger is going to use these claws seriously. The math for a necklace of natural attacks that affects two claws works out the same as enhancing two 300-gp base-cost manufactured weapons the same way. Note that Magic Item Compendium allows you to add various generic bonuses to magic items without the usual 50% surcharge, so the necklace of natural attacks can also have, say, an enhancement bonus to Constitution just by adding the cost of a periapt of vitality to it.
If the necklace of natural attacks is unavailable, an amulet of mighty fists +1 is sufficient to allow the claws to overcome DR/magic (i.e. to make them worthwhile at all), but further improvements to that item are drastically overpriced. In fact, it may be much more effective for the weretiger to get DR/magic of his or her own, since
Some monsters are vulnerable to magic weapons. [...] Such creatures’ natural weapons (but not their attacks with weapons) are treated as magic weapons for the purpose of overcoming damage reduction.
(Special Abilities > Damage Reduction)
But realistically, without necklace of natural attacks, it’s probably best to just give up on the claws altogether.
If the weretiger can somehow transition to aberration, dragon, elemental, magical beast, or plant type (this would have to happen after acquiring lycanthropy since lycanthropy only applies to humanoid or giant type creatures), then the Rapidstrike and Improved Rapidstrike feats are must-have high-level feats, since they effectively give your claws iteratives. Going from two claw attacks to four and then six is a big deal, even if does take 12th and then 15th or 18th level to make it happen.
Beast Strike, and using unarmed strikes
Beast Strike is a very weird feat from Dragon vol. 355 that lets you add your claw (or slam) damage to your unarmed strike damage when making an unarmed strike. It’s not clear exactly what this means (for instance, your claw damage would typically include your Strength bonus; do you get to include that, and effectively add it twice to your unarmed strike?).
But no matter what, it’s a solid feat for a weretiger, because you are using your claws while making unarmed strikes. The important thing here is that unarmed strikes get iteratives.
Going to require Improved Unarmed Strike, obviously. Snap Kick in Tome of Battle lets you take a −2 penalty to all attacks in order to attack once more with an unarmed strike any time you could attack at all. I.e. attack of opportunity, martial strike, whatever. If you get at least one attack, Snap Kick gives you another one. When doing a proper full-attack, they’re also compatible with Two-Weapon Fighting et al. which could be a good option for the weretiger. And Superior Unarmed Strike, Tome of Battle again, can improve that unarmed strike damage (only worthwhile pretty late though).
By the way, barbarian already comes highly recommended for this weretiger, and the city brawler variant in Dragon vol. 349 adds Improved Unarmed Strike and Two-Weapon Fighting (but only for unarmed strikes) as completely-free bonus feats.
Martial Study, if not warblade or bloodclaw master
Martial Study grants a single martial maneuver from Tome of Battle, and the Tiger Claw discipline is, unsurprisingly, awesome for a weretiger. You can take the feat up to three times. Sudden leap allows for some swift-action movement, wolf fang strike allows a dual-claw attack as a standard action, and dancing mongoose and raging mongoose allow those claws to attack more. In fact, considering how excellent Tiger Claw is for you, the weretiger should absolutely be taking levels in warblade, and quite possibly the bloodclaw master prestige class, from the same book, as the former gets access to Tiger Claw and the latter specializes in it.
If restricted to just feats, wolf fang strike, sudden leap, and dancing mongoose, in that order, is my recommendation. The first two can be gotten at any level, but the last is going to require 18th if you don’t have any initiating levels.
Worth noting: Martial Study can be taken by a fighter as a bonus feat.
Power Attack and Shocktrooper
Shocktrooper is a feat in Complete Warrior that allows you to use Power Attack but penalize AC instead of attack when you’re charging. Charging is good for a weretiger in general, and this allows Power Attack to be worthwhile (losing 1 attack for 1 damage is pretty meh, but losing 1 AC for 1 damage is much better).
Note that Shocktrooper also requires Improved Bull Rush. The weretiger will most likely just about never use it, but Shocktrooper is still worth it. If someone’s stupidly-close to a cliff, a bull rush just might be a good idea.
Leap Attack from Complete Adventurer allows you to count any jump of 10 horizontal feet or more as a charge. This makes charging far more flexible, and even if this was all it did, it would be worth it, but it’s actually better than that: it also doubles the bonus damage you get from Power Attack. Losing 1 attack for 1 damage is pretty meh, but 1 attack for 2 damage is pretty solid, and losing 1 AC for 2 damage with Shocktrooper is excellent.
Arguably allows charge-as-a-swift-action with sudden leap; this is probably something any sane DM would nix, and this weretiger probably shouldn’t need it, but there it is.
Not worth it: Improved Natural Attack, Improved Critical, Weapon Focus et al.
These are various common, generic feats, that can be applied to claws. None of them is really worth a feat here; they’re small, incremental improvements that a weretiger should not need. The only exception is if they are used as the requirement for something better; in some cases, it can be worth it to burn a feat to get access to something juicy later, but then the requirement for one of these feats should be considered a very steep cost for that thing.
Warblade, maybe bloodclaw master
Warblade is an excellent class in general, and it’s fantastic for a weretiger. And, especially nice, you can get the class completely free and legal from Wizards’ website, and you can get all of the maneuvers, too, so you don’t even need Tome of Battle. Just know that to use a maneuver of Xth level, you need an initiator level of 2X−1 (same as a wizard for Xth-level spells), and your initiator level is your class level plus half your level in other classes (including racial hit dice).
The warblade is nice for a lot of reasons, but Tiger Claw is particularly what you’re looking for here. Wolf fang strike, sudden leap, dancing mongoose, and raging mongoose have already been mentioned, but deserve mentioning again. And beyond Tiger Claw, several of the other disciplines have useful features.
Diamond Mind has moment of perfect thought which allows you to replace a Will save with a Concentration check (note: Concentration depends on Constitution, which is probably much better than Wisdom, and you can put a rank in Concentration every level, while even the good Will save progressions only go up once ever two levels)
Iron Heart has punishing stance, for more damage, and iron heart surge, which lets you just flat-out end any one negative status condition or effect.
Stone Dragon has mountain hammer, which ignores DR and hardness, going through tough enemies as well as things like walls and doors with ease
White Raven has battle leader’s charge, which adds a fairly significant wodge of damage to charges. Charges can be very good for you (see barbarian, below).
And that’s just at low levels. Warblade lets you get all of these.
Now, Tome of Battle also has the bloodclaw master prestige class, which focuses exclusively on Tiger Claw maneuvers. It also has a strong shapeshifting theme, which is extremely appropriate for a weretiger, and it has a lot of useful features for dual-wielding. But the loss of the other disciplines is a harsh blow to any warblade. Definitely get at least one level of warblade for the recovery method and to pick up stuff like moment of perfect mind and mountain hammer before doing bloodclaw master.
A single level of barbarian has a ton going for it. If you have Complete Champion, you can trade Fast Movement for Pounce (full attack after a charge), which is absolutely amazing. Rage itself is awesome, and Whirling Frenzy makes a strong case for being even better. A second level can, if you use the Unearthed Arcana variant, get you Improved Trip without needing Combat Expertise, which is awesome; less great for a weretiger than it might be, but still awesome.
If going with Beast Strike, the city brawler barbarian in Dragon vol. 349 grants both Improved Unarmed Strike and Two-Weapon Fighting for unarmed strikes for absolutely free. This is a very solid option as well.