Argonians and Khajiit are good for stealth type characters since they start out with higher skill levels in sneak. Both have bonuses to unarmed attacks and Argonians can breathe undewater (as well as resist diseases a little better.) Redguards can resist poison somewhat, have skill levels in combat and certain magic types, and just look cool.
Really there isn't much difference. NPCs will address you differently but don't treat you differently as far as I know. I do think that the height of characters affects movement (and therefore sprinting/walking speed).
Try here for a look at the differences: http://www.uesp.net/wiki/Skyrim:Races