check out this thread for starters:
http://www.minmaxboards.com/index.php?topic=2773.0the Truenamer is a terrible class that should have gotten more love. Everything that "fixes" them is all homebrew, but if your cool with that some stuff is interesting.
for my own experience I experimented with something like the spell to power psionic rules as homebrew truenamer rules.
I didn't quite get the balance right, but I made it so that anything that affected targets could be converted into a true-name effect-and even multi-target spells could only affect single targets until 13th level.... there was a material cost for conversion, like 50gp per spell level- and I allowed a spell from any domain to be converted.
The save DCs were equal to what the truenamers normal DC effects are, and the truenamer check was 4x spell level, and you couldn't learn the spell unless you were 2xthe spell level in character level.
some stuff seemed balanced and some was too overpowered... I'm not sure a straight 4x Spell level is the best conversion method. ends up being a 36 DC for 9th level spells which may be too strong.
there's also a truenamer handbook floating around here, but I didn't think it was very good, as it mainly just tells you to max UMD and use items to make up for your handicap...