Try looking for ASIC-proof crypto-currencies; those where it's not (yet) possible to imitate proof of work with special computing devices designed specifically for mining. The ones I know of are Primecoin and Monero. Both have been around long enough for the difficulty to climb through the roof and, as far as I know, both have been "cracked" to allow GPU mining. Thus laptop users are out, but PC users with a decent video card can still get earn a few pennies. Not much to really get rich (perhaps - hardly enough to pay the power bills) but if you already have a PC and use it anyway for your day to day stuff, then you might as well have the mining app running in the background, whatever it mines - is all yours.