Actually some of the best character skill systems I've seen are in Vampire: The Msquerade - Bloodlines and Arcanum: Of Steamworks and Magick Obsucra. Arcanum in particular, what they have in common is that when you level up/get experience it's given to you purely in the form of points to spend on abilities, which are all clearly spelled out from the start so you know what you're building.
To further explain, I really liked the system used in Arcanum because the levelling mechanic worked on a very simple system which still allowed you to build a huge variety of very interesting characters. The way it worked was that when you levelled up, you got a point to spend on something. Anything. High level skills weren't inherently more expensive than low level skills, but were kept balance by the fact that they required a higher stat in order to be able to get them. These stats were built up through the same system...
Look, to be honest I can't properly explain it properly anyway, I just liked the fact that every possible skill or ability was presented as an equally valid choice and that you could plan out a character build without having to worry too much about putting a couple of skill points into other areas[footnote]Sadly the game never really delivered in the combat area which made part of your character build less important, but it was still a great system.[/footnote]. Compare this to D&D, for example (I refer to 3.5 edition, just because it's all I know). When you were playing that, after you'd made a character and picked out their race, class, abilities, skills and feats at 1st level they were pretty much set upon a single path with no significant changes along the way.
