Random loot tends to be very aggravating for players unless they either specifically enjoy that wealth paradigm, you're using a module to run a one-shot, or they have some method (typically an Artificer [Eberron Campaign Setting] in the party, or another crafter who can take gold from selling magic items) to turn random loot into non-random loot. Wealth does have the power to affect balance - too little and it restricts the kinds of enemies you can throw at the party, too much and your players are above the curve for a lot of level-appropriate monsters. Here's some suggestions:
Know Your Monsters
Some monsters require certain kinds of magical items to fight, depending on the character. Do you use a lot of monsters with DR/Magic? Maybe after a fight or two like that, it's time for your PCs to find a magic weapon. Lots of flying monsters? Then access to flight (for melee) or magical ranged weapons (for archers...well, for that matter, also for melee) would probably be appreciated. In some ways planning ahead can help you with this - for example, if you hand out a magical cold iron weapon now, your players are partially equipped to fight fiends later.
You Could Let Them Pick
The Dungeon Master's Guide contains tables for average WBL, which in a "standard" campaign is the guide to about how much GP worth of magical and nonmagical crap the PCs should have. One technique that's worked for me in the past is to give the players wealth that's roughly equivalent (maybe some gems or fine art works - if anyone has Appraise, let them use the skill to wring a few more gold out of the sales) and let them purchase their own magical items. Temple armories, local Artificers (or Wizards, or Warlocks) and/or the vaults of adventurer-friendly organizations (like the Knights of the Chalice [Complete Warrior] in an anti-fiend campaign, or the Mages of the Arcane Order from Complete Arcane) can provide a funnel for that wealth without making it seem like one or two people are running MagicMart. Mind you, if you're running a setting where MagicMart is appropriate (Planescape, Eberron, maybe a custom setting) then by all means, turn them loose on MagicMart. By restricting their wealth to the value(s) on the table, you prevent them from grabbing anything that the game doesn't already "expect" them to have available.
There's Items Everyone Wants
Some items are considered "essential" by the community's examination of monster math. Most notably, ability score boosters (Headbands of Intellect, Belts of Giant's Strength, Bracers of Dexterity, Periapts of Wisdom, and the like) are desired by every character in their primary ability score and will often be worn for secondary ability scores as well. For spellcasters, these item boosters directly translate into more spells at higher save DCs. For melee characters, these item boosters mean accuracy and damage (for some classes, secondary items might boost save DCs or minor benefits, such as a Warblade's intelligence-keyed abilities). Melee characters want items that provide flight (Wings of Flying), swift-action movement (Anklets of Translocation [Magic Item Compendium]) and/or defensive utility (Blindfold of True Darkness [Magic Item Compendium]). Spellcasters, on the other hand, usually like things that extend their resources - like wands that cast valuable buff spells for them (try to pick ones with long durations, like Mage Armor or Bull's Strength), metamagic rods (empower is a great choice, and you'll find them in both the Dungeon Master's Guide and Complete Arcane), Blessed Books and the like. A lot of times you can afford to give kooky stuff like a Ring of the Ram to a spellcaster just because they are magic and can thus afford to get away with things that don't necessarily boost their own resources. If you and your group is new, this advice will last you awhile; if your group develops an interest in high-op play, I'd suggest coming back and asking about this subject again.
Monster Loot: Generic Grunt Edition
The various Monster Manuals provide a rough guide on when generic mooks start picking up magical items, and you can also look into modules like Expedition to Undermountain for a rough guideline as well. Generic mooks with magical loot are essentially good for two things after the fight: providing the party with raw wealth to be turned into more/better items in town (see above) and replenishing resources like potions and scrolls that the game expects them to have on a semi-regular basis. At low levels, these generic mooks might also provide them with starter items like their first magical sword, a suit of enchanted armor, or the like. The thing to remember is that at higher levels, what qualifies as a generic mook now was a campaign Big Bad Evil Guy a few levels ago; at higher and higher levels, the mooks are less "generic" and more "well equipped special forces who happened to pick the wrong people to fight." Don't be afraid to equip your mooks better once it becomes appropriate.
Monster Loot: Lieutenant Edition
Named antagonists can, of course, carry better or more relevant loot. Maybe the Blackguard serving the lich at the center of your campaign wields a Screaming Greatsword that the party Warblade might lust after. The module Ruins of Myth Drannor had an example of a unique-seeming weapon in the form of a Frost sword covered in Continual Flame spells. Lieutenants, at lower levels, are also a source of higher-class disposable resources like wands and high-level scrolls, might provide spellbooks encoded with new magics, and depending on their specialty (magic, melee, archery, skillmonkey) may have other nifty tricks like metamagic rods, enchanted thieves' tools, weapon crystals (a very handy type of item out of the Magic Item Compendium that I highly suggest to you), and the like. I have a special fondness for giving my players extradimensional storage space (Bag of Holding, Portable Hole, Handy Haversack) by looting it off of lieutenants.
Monster Loot: Boss Edition
Dragon hordes! The armory of an evil fortress! The magical wealth arrayed around the deadly lich, now ripe for the plundering! Bosses are your chance to hand out minor-seeming essential items, either on the dead boss or socked away in a treasury as a magical curiosity. They can hold things like Blessed Books, higher-end stat boosters, Ioun Stones, and the like for you to give to the triumphant heroes. Bosses might also hold items of powerful and dangerous natures (like most cursed items) that the PCs can turn over to temples or good-aligned organizations for a monetary or magical reward that can then be turned into the wealth they want. If you don't mind PCs being slightly above the curve, bosses can provide small magical tricks that are handy, but not particularly powerful - things like a Ring of Arming. You might even sneak a plot hook or two in.
Monster Loot: Assassin Edition
Special consideration should be given to the point of balance between "faceless expendable" and "lieutenant" in the form of assassin or special-forces class enemies. These guys are better equipped than mooks, usually operate in teams, hate your PCs and want them to die. Assassin encounters have their own pitfalls and flaws (which I won't get into here) but they're useful for handing out specialized equipment that doesn't really cost a lot, but also doesn't see use outside of, well, adventuring and assassination. Items like Blindfolds of True Darkness, Anklets of Translocation, martial scripts (Tome of Battle), and other niche things that make you think, "Who uses this outside of adventuring?" are a good fit for most assassin-type encounters and might be a good way to introduce a character to a utility item they didn't even know they wanted.
One Last Thing
Being conservative with wealth isn't a bad thing if you're willing to adjust it once you realize you've gone too low. It's always possible to give wealth away, but much harder to take wealth back once you've granted it to your PCs. Start low, then slowly increase the amount of available wealth until you find a sweet spot for your game - then live in that sweet spot and don't leave it until or unless you start a new game! In 3.5, wealth is very literally power, and should be handled with the care and respect that implies.