Another game I would give high marks in variety to is AC1. Some combinations of abilities were not even discovered until a year or so into the game. The only bad part was that some of these builds that were discovered were not really capable of doing damage, ergo leveling until something stupid like level 90. I hear that they implemented full respec now, which probably changes things for the better in that regard.
AC1 is really incredible for the variety of builds out there - the only thing limiting you oftentimes is your imagination. I met guys that had specialized Sword and War Magic, or fought only with Life Magic, or all sorts of other weird combinations - and yet, you could usually make something effective and working with it.
AC1 and UO are, IMHO, better models for the future than the 'hard classes' approach favored by DAoC, WoW, etc.
Though to make this WoW related, since you're right, I feel bad about bringing up AC here: One thing I liked in WoW (and that was perhaps more significant to me since I never got beyond level 6) was that the different races started you out in different newbie areas, adding another level of differentiation beyond just what class you selected, and making it so the race you pick isn't just about what bonuses you get. Everyone having their own unique "Homeland" memory, of 'this is where my character comes from', is cool even if past a certain level I'm sure you don't really feel it in gameplay terms.