It depends what you are looking for. Quick money, big money, or sustainability.
I like Neobux.com. It is slow to build, not very many ads for standard, but very sustainable and offers instant pay at $2 through AP and PP.
Also like TakeTheGlobe.com. Standard only pays .005 and .0025 for refs but that makes it very sustainable. I think both will be around for awhile so they are investable.