Tier Numero Uno: Olaf, Fizz, Gangplank, Lee Sin, Tryndamere, Cho'Gath, Udyr, Nidalee (warmog's + atma's), Renekton, Trundle, Irelia, Riven, Rumble, Gragas
Tier Numero Dos: Volibear, Garen, Yorick, Morgana, Kennnen, Maokai, Skarner, Talon
Tier Numero Tres: Wukong, Jax, Singed, Shyvana, Nasus, Akali, Teemo, Pantheon, Swain, Galio, Malphite, Sion, Jarvan IV, Warwick
Tier Numero Cuatro: Urgot, Mordekaiser, Vladimir, Nunu, Alistar
Tier Numero Cinco: Anyone else, minus Evelynn.
Tier Numero Seis: Evelynn.
Tier Numero Uno: These champs rape face. They have it all: tons of sustain, mobility, and damage, a great early, mid, and late game, and don't need two summoners, so you can afford to use teleport for more map mobility. Can definitely carry games with these guys.
Tier Numero Dos: These champs are almost as strong as Tier 1 picks, but they lack either some sustain, damage, or mobility that Tier 1 picks have. These are great picks to carry games as well, but some Tier 1's can shut them down.
Tier Numero Tres: Many of these champions lack the sustain that the Tier 1 and 2's have, don't have a great lane presence early game but make up for it later, or fall off later in the game, but have a pretty easy time laning. Still very strong picks, but not as well-rounded as Tier 1 and 2 champions.
Tier Numero Cuatro: These guys work, but are better in other places, for various reasons (need blue buff, are better in another lane, etc.). Some of these champions would also supplant your damage melee DPS top, which may not work with many team comps. Most of these champions also don't have very heavy sustain, especially pre-6, if any at all. Can work, but hard to fit in.
Tier Numero Cinco: No. Put them somewhere else.
Tier Numero Seis: AW HELL NAW. *passes out on floor*