This is some of my favorites that I have actually seen used on the internet:

Stick=Schtick
Pre-Madonna=Prima Donna *
Mute Point=Moot Point
Looser=Loser
Laundry Mat=Laundromat *
Baffoon = buffoon
Noone=no one
Hugh = huge
juggler = jugular *
Out of Sink = Out of Sync
Lakeperson=Lay Person *
Dirty Mined = Dirty Minded
balled or bold-faced liar = bald faced liar *
Infactuated = infatuated
annie up = ante up
death kneel = death knell *
quick claim = quit claim
whipping board = whipping boy
beseige = beseech
water under the fridge = water under the bridge

Any others?

*classics

I purposely left out some common annoying mispellings/misuses such as:
Your-you're
There-their-they're
Know-no
Want-won't
to-too