i finally put the money and time together to build a kegerator. i am very happy with it overall. it is based around a kitchenaid KURS (kurs24rsbs) undercounter mini fridge that i bought on craigslist. the top is edge-glued aspen from lowe's. i doubled the thickness of the board to allow for the drip tray plus to make room for the fridge door hinge. the kegerator top is affixed with l-brackets that i recessed into the bottom of the wood counter. i pulled the rails and drip tray from a broken beverage-air kegerator. it holds two five gallon kegs, one three gallon, and a co2 tank.
Edit: I posted the above immediately after building the thing. It wasn't long before I noticed a foaming problem because of the temperature differential in the tower (much like many others have identified). A great thing about this particular minifridge is that is is a legit fridge with an evaporator fan, etc. So unlike most minifridges, this one has a fan circulating air when the compressor kicks on. So rather than add a cooling fan, I simply took advantage of the existing fan. I felt around on the back panel for a place with nice airflow, drilled a 1" hole through the plastic rear covering, and inserted one end of my flexible tubing in that hole as a means of securing it (perhaps it could be taped instead) to the back panel and after confirming some airflox through the tube (not much really), I pushed the other end up into the tower. This simple change has made a world of difference, eliminated the foaming problem, and really turned this into a first-class kegerator.
You can see the white flexible tubing (just barely) towards the top of this picture. You can also see how I fit a 5lb co2 tank, two five gallon, and one three gallon keg in here.
If you happen upon a KURS kitchen aid undercounter fridge, it can be made into a truly amazing kegerator. Mine is the only conversion of this model i've seen, probably because it retails for just north of $1,000 (mine was a craigslist score at less than 10% of that price).