Fast troops, with all Knights having an 8" move, 16" charge. Great melee fighters, are devastating on the charge (hitting at S5 and S6 with only a 3 man front) and almost all knights have a 2+ armor save .
Other potential armies: Chaos (Khorne); not as fast, buy Chaos is the best close combat army in the game according to most (but I still think Bret's can be better if used properly)
High Elves; the all cavalry High Elves are very popular at the moment (I dare say moreso than their footslogging bretheren). Also, Elves in general have better movement stats then most. Only thing about HE is that they are almost certainly the next army to get their army book redone/rebalanced for 7th edition. However, these guys will not be as strong as Bretonnians on the charge because of a lack of the "lance formation"
If you need any more help with either Brets or HE, feel free to drop me a PM or post in any of the army forums. Brets were my first army, and I'd be happy to lend you any advice I can. Good luck with your choice, I hope you find the army that works best for you.
EDIT: Oh and if I've forgotten an army that should of been listed please feel free to add it. The only one I feel that could have possibly been overlooked is DE and that is because I have no experience with or against DE so I really can't comment on them at all.