I would highly recommend simple "new" sites that are easy to copy.
The day blackle was posted (i believe here) my buddy created earthle.com, he had it up in running in under 10 hrs I'd estimate.
Since then it has been making him anywhere from $40-$80 a day and what are his costs...$20 bucks a month hosting!
Nothing like a sweet monthly check for doing absolutely nothing!
G33ks