D&D 3.5 may not be the most recent version, but it still has quite the following. Recently, when leveling up my Sorcerer, I looked in a friend's Complete Scoundrel
(a source book for Rogues) and discovered the existence of something called "Skill Tricks." These are very similar to Feats, but revolve around Skill Ranks (something that everyone gets, but none so much as Rogues). While explained in the Rogue's source book, they look like they could prove interesting and perhaps useful to others. Of interest to my Rogue were "Collector of Stories" and "Conceal Spellcasting."
If you're not building a character with Skill Tricks in mind, however, you may find it daunting to try to determine what Skill Tricks you already qualify for... or how far your character is away from various Skill Tricks. Fret no more - this handy calculator will let you know exactly where you stand on meeting the various Skill Trick qualifications.