Adding Dexterity to damage
The Dead Eye feat from Dragon Compendium lets you apply your Dexterity bonus to your damage with ranged attacks. Note the errata for Dragon Compendium that reduces the BAB requirement to +1 (instead of +14!).
The Crossbow Sniper feat from Player’s Handbook II adds half your Dexterity bonus to your damage with crossbow attacks. Crossbows are difficult to use, but this feat can be a decent reason to try. See this answer for more on making the most of crossbows.
The hit-and-run tactics fighter alternate class feature from Drow of the Underdark allows you to add your Dexterity to damage when attacks flat-footed foes. Making foes flat-footed is pretty tricky, but if you were using sneak attack, you were going to have to do that anyway—this is a pretty big bonus on top of sneak attack for doing it.
Increasing your Dexterity
Enhancement bonuses to Dexterity, e.g. from gloves of dexterity, are a high priority for you. You should have the largest enhancement bonus you can afford just as soon as you can afford it.
A racial bonus to Dexterity is less important. Particularly if it means not getting a bonus feat, or taking a penalty to Constitution.
Beyond that, one of the biggest chunks of Dexterity in the game is from the wildrunner’s primal scream, which works kind of like rage. Wildrunner is from Races of the Wild.
Adding something else to damage
Sneak attack, as mentioned, is traditional, though getting foes flat-footed for it is difficult. If you go that route, definitely also grab hit-and-run tactics and the Craven feat from Champions of Ruin.
Knowledge Devotion, also mentioned, is definitely worth grabbing. It’s solid bonuses to attack and damage, and it’s pretty inexpensive.
Hank’s energy bow from the obscure D&D Cartoon DVD’s booklet on the main characters is also reproduced on their website. It effectively gives you Power Attack with your arrows. That can potentially be a pretty serious amount of damage, though sadly you do not get the 2:1 returns that Power Attack does with two-handed weapons.
Adding Charisma to damage is available through a variety of methods, such as the hexbands from Magic Item Compendium, or the Divine Might feat. Notably, Charisma can also replace Dexterity on bow attack rolls via Charming the Arrow, though between the need for Dexterity for archery feats and the various options for adding Dex to damage, I’m not sure it’s worth it.
Along similar lines, but almost-certainly not worth it, swordsages from Tome of Battle can add their Wisdom bonus to damage rolls made as part of strikes made from a chosen discipline. Not many of those strikes are compatible with archery, but if you choose carefully you could maybe do it. You can replace Dexterity with Wisdom on ranged weapon attack rolls with the Zen Archer feat from Complete Warrior.
Getting more attacks
The traditional route to archery damage is just by having a huge number of attacks.
Rapid Shot is the obvious example of this. Manyshot is not, however, as it only lets you apply bonus precision damage to one of the shots and it eliminates any other bonus attacks you might have (e.g. the one from Rapid Shot). Greater Manyshot fixes the precision damage limitation, though you still do not benefit from other bonus attacks.
The whirling frenzy rage variant can give you another attack.
Haste gives you an extra attack, if someone would be kind enough to cast it on your party (they should, it’s one of the best spells in the game). If not, a speed weapon could suffice.
Speaking of weapon properties, splitting from Champions of Ruin turns every arrow into two. Which means it doubles your attacks, including all the extra ones. It even works with (Greater) Manyshot. It’s a +3-equivalent, but it is so very much worth that.