Well, for sorcerers a level of candle caster is very helpful as a kind of "stepping stone" to wizardly PrCl's. It gets all knowledge skills and a virtual item creation or metamagic feat (in an alternate medium) at every level.
For fighters, gladiator is easy to get into, and it has some useful skills and a good reflex save. Being able to use bluff in combat as a move equivalent action can be a real asset at times.
3 levels of ranger (3.5) and one level of templar is a way to get weapon specialization without taking 4 levels of fighter. Mettle, a spell, and a bonus to will saves is just a bonus.
A level of Palemaster gets your wizard a boost to fort saves and +2 Natural Armor, with no sacrifice of spellcasting ability. A level of Mindbender gives you telepathy, a similar boost to fortitude saves, and some good skill boosts.