Pantheon can pretty much do everything well except adc. He CAN adc, it's just early game can be a bitch if they're too agressive.
Vi. Sounds crazy but she can top well with flasks+pots (refer here and read the comments: http://boards.na.leagueoflegends.com/en/c/miscellaneous/MBTEAJ7A-vi-top-help-modify-build-long), she can mid against many (most?) champs if you play safe until you rush an early hexdrinker/maw, jungle is obvious, and her shield passive, Q cc, and early damage make her both a viable support for either aggressive or safe adc, and an adc herself if your support is aggressive enough.
Xin Zhao can do it all (though again with trouble ADCing). You can take him squishy damage, full tank, or even AP/Attack speed to exploit the insane healing of his W passive, and all while providing insanely useful utility to your team.
I personally suck at Cho'gath, but if you do well with him, he's yet another all-except-ADC champion.
Fiora is freelo. She is squishy (early) and kind of shut down by cc, but if yoit lane isn't against any heavy stuns she can do everything, even ADC well (For a squishy melee I am frequently surprised at how well she adcs when she takes extra armor runes and her W is maxed first).
Fizz, for the moment, can be taken anywhere. Whether AD or AP, he's going to dominate by or before the mid game. His support game is kinda dry, so maybe refrain from that role, but if your adc is aggressive he'll do fine. A full build, tanky, lifesteal AD Fizz destroyed me 1v1 as a full build Udyr with 90stacks of devourers.
Heimerdinger can do all except jungle. No explanation necessary.
I'm getting bored so here are just a handful of champs that can do at least three roles. I know this account is in bronze 4 but I'm a gold 1 player on one smurf and up to gold v on another. I'm just barely above average at this game, but the champions I'm listing above and below here are tested. They really do work if you adjust your runes and items depending on which champion you're laning against:
Nidalee, Jax, Karma, Kennen, Kayle, Orianna, Sion, Teemo, Yasuo
Sorry if I left someone out. Point is, season 4 was.. and so far season 5 is... a silver age of "balance;" less champions are crippled playing against all champions in a certain class (tank, fighter, etc) and now mostly just by certain attack type (AD/AP Burst, CC, etc). It's made many champs viable to go against more variety of champs than they ever could before.