Two of my favorites:
Child of Shadow stance - Level 1 Shadow Hand stance, so a 1 level dip in Swordsage or 2 feats (you need Martial Study for a maneuver before you can get a stance) gives it topretty much anyone. Anytime you move 10+ ft in a round, you get 20% concealment until the start of your next turn. From Tome of Battle.
Shadowcraft Mage - Prestige class from Races of Stone for gnome illusionists. At 1st level it grants a continuously active (free action to dismiss or resume) "cloak" of shadows. It only functions in areas of shadow, dim light, or no light, but low level spells can make that "99% of the time." Gives you a miss chance of 15% +5% per class level (max of 40% at class level 5, it's only a 5 level class).