Ahri is good, same with lux. Lux is actually pretty overpowered now since they made Athene's.

I also love ahri and kat and my other favorite pick mid is kennen. he is awesome. another good one apart from that is tf if you have good map awareness.

depends on team comp, i love picking orianna with an initiator like shyvana/malphite/or amumu on my team.

kat, diana, are pretty safe and beastly picks, but you gotta get close

karthus and lux if you wanna crush from a distance

malz/galio are good counterpicks

ap cho mid is hard to push outta lane and has incredible cc, also gets really tanky and bursts REALLY hard

cass and brand are both tons of fun, i'd hold off on lb. she either carries hard or fails hard.

mord/ryze/ap teemo/tf - also all tons of fun

find your style or just buy em all!

Galio, takes practice with him but he is absolutely the best ap mid in solo q

Twisted Fate is very strong and personally one of my favorite mids.
Gragas is really good.
Anivia is incredibly strong, and with an early blue buff can shut most anyone down.
Vladimir is strong after level 9, and his sustain becomes unbeatable.
There are many mid champs that are strong, you just have to find the ones you like!!