yea get irelia and see if you don't regret like 70% of the people who brought her(recent forum vote result)
but personally i would choose Renekton for sure, since he have leech, escape ability(direction dash+dice if you hit something).. and stable stun... irelia's stun only work if she have less health then her target, and she get to choose one between slow and stun...
Renekton's problem was his damage was a bit low.. but serious irelia isn't any better.. irelia's Q scale to ad, E scale to ap.. and W need frozen mallet and aspd stuff to do damage.. ult are only useful for farming creep with 40 second cool down..(it have 0.5 refresh time, so will hardly ever hit two person after the first hit... unless you only play against new player[80% of the player i play against know and can dodge her ult easy... the other 20% might now fight irelia before.. since she is very rare chosen in both rank and normal..])
p.s. Irelia is the worst choice by far i blieve, grab Xin is you like her style.. Irelia is just an inferior clone of Xin for now...