Ahri: good farmer, good range, strong farmer, super-strong cc, 3-flash ultimate means you can be ballsy and also means only the strongest ganks can kill you.
How she plays: Skillshots, kiting, level 6 ult bumrush burst makes people go WTF?
Cassioepia: good farmer, terrific harass, good kiting, sustained damage, powerful cc ultimate
How she plays: Lane bully, strong zoning, and BITE BITE BITING ( E spam ) if you land a Q. Aggressive champ with powerful sustained damage can get ridonculous.
Xerath: good farmer, safe harass, ridiculous burst at level 6, ranged stun, aoe wins teamfights outright.
How he plays: BZZT BZZT in lane. Catch opponent with E->Q stun combo and proceed to bzzt more. When ultimate comes lay the smackdown on your enemy or the entire team. With ridiculous range in W siege-tank mode you never have to put yourself in harm's way. Snipe snipe snipe.
Ryze: great farmer, great harass, good range, tanky mage is all about comboing one spell off another in a machine-gun fashion.
How he plays: Farm the tear of the goddess, come back in lane wailing on your opponent on anyone cuz the more you spam the harder you hit. Spam all day and profit with fantastic defensive items ( glacial shroud, banshees veil ) and keep on chucking those Q's cuz you are one mean mofo.
Leblanc: Super damaging burst, blink escape, ranged cc
How she plays: Get to level 4 or 5 or even 6, **** on your opponent. Ridiculous burst damage means you snowball and drop people from 100% to 25% health in under a second. Falls off late game but if you press your advantage being the scary ***** that you are, game should be over mid game.
Morgana: great sustain, great farming, can't be killed, strong teamfight ultimate
How she plays: Farm and heal at the same time. Morg is never low on hp. Someone casting something... cc perhaps? Black shield, laugh in their face. Great snare on top of team-wrecking ultimate can make for completely one-sided teamfights.
Swain: strong harass, great farming, aoe snare is strong, 2 forms of cc ( 3 later ), ridic sustain.
How he plays: With your E + auto attacks you are a bully. Your W snare has such a long range that landing it on one person or several is really easy if you actually practice. You're one scary bird that ults and does constant damage to 3 people around you while you can keep 1-3 stunned and 1 more slowed by a ridiculous amount. Very strong against melee as they can't chase you. Tanky ap caster with a huge teamfight presence. He's also fun to play.
Try out swain, get good with him, and you will wreck people.
I find that I have a very very very hard time last hitting with Swain.
Strange, he's got a great attack animation and for a caster he seems to hit minions kinda hard. If you have that much trouble consider going 21 into the offense tree and even picking +4 dmg to minions to help you last hit. May seem like a huge sacrifice but considering all the cs you're missing out on pre level 6, it's really worth it if you can't last hit without it.