The most thorough option (but also horribly overpriced)
The 3.5e drunken master prestige class from Complete Warrior gets a feature, stagger, that eliminates the restriction on turning from charges entirely. It’s literally the only good thing an otherwise atrocious prestige class gets. Most of the rest are actively harmful to use and should be ignored even if you have them, and the class is very painful to enter.
A quite limited option (that is extremely cost-effective)
3.5e’s Complete Scoundrel printed skill tricks, which were kind of like mini-feats that you could obtain by spending 2 skill points, rather than waiting for one of the levels in which you actually got a feat and spending one of those few precious opportunities on something. Skill tricks tended to be weaker than feats, and in any event you could never use one more than once per encounter, but 2 skill points is still super-cheap.
One of those skill tricks is Twisted Charge, which allows one turn of up to 90° during a charge. Again, that’s once per encounter. Still, encounters with multiple charges are somewhat rare, and most of the time turning isn’t terribly important, so it’s very easy to imagine going many combats without ever needing more than this.
And then there were the feats
There are a bunch of feats that allow turns on a charge, usually just one each, usually limited to 90° but you could take multiple to allow more turns (though probably not sharper turns).
Bestial Charge (Complete Champion) allows you to turn once every 10 feet on a charge, with no limitation on how tight a turn, but only when wild shaped into a quadruped form.
Fleet of Foot (Complete Warrior) allows a single turn of 90° or less, and requires that you not be wearing medium or heavy armor and that you have travel at least 10 feet in a straight line before finishing your charge with an attack. (Technically, Player’s Guide to Faerûn included a totally-separate feat called “Fleet of Foot” and since it came after Complete Warrior, by the rules it replaces the Complete Warrior version. But that’s pretty clearly just an editing oversight.)
Mantis Leap (Sword and Fist) allows you to trigger a charge against anyone you can make a Jump check to reach. Extremely unclear about how that actually works, but it seems to basically be saying that if you make the check, you’re eligible to take a full-round action to charge that creature (even if conditions on the ground would otherwise prevent it). Vastly simpler ways of wording this were available, and the wording used potentially allows arguments for all kinds of other things, but all it probably means is that you can jump on a charge (which you can probably do anyway).
Psionic Charge (Expanded Psionics Handbook or here (or here for Dreamscarred Press’s Pathfinder version, which is identical) lets you make a single turn of up to 90° by expending psionic focus.
