I've got a Frigidaire 8.8 cu ft from Lowes. Like I said, i can fit 7 ball lock kegs and my 5# co2 tank.
Even if you only want a 4 tap keezer, I highly recommend getting something big enough to hold 5 kegs. Also get a 5-way co2 manifold. That way you'll always have a keg ready when one goes dry. Also if you ever decide to add a 5th tap, you can. I originally just wanted 5, but I'm finding that I'd like more. Now I'm really glad I have the option of adding two more.
Sort of like a TV. I always tell people go one size bigger than you think you want. The only person who hasn't listened to me is my dad, and he regrets it.