I used to have a WetJet but the whole system is expensive. First the mop is around $20, then you need special swiffer pads, then you have to buy their solution. I found it quite ridiculous.
I found a really neat item from Bissell called a FlipIt. You can vacuum with one side and mop with the other, and it comes with microfiber cloths that are washable so you don't have to buy those Swiffer pads. It comes with their hardfloor cleaner, but when I run out of that I'll be using Mr. Clean in it. Filling the tank is really simple. I love it!
http://www.bissell.com/Products/c/bare+floor+solutions/p/flip-it/product.aspx