I have 'student loan' domain parked at parked.com. the result was just ok. RPC not too high as well, ranging from 0.20 - 0.40$. Perhaps you could try Adsense for Domains? They have 1 landing page, compared to 2 landing page at parked.com. however, with parked.com you get the advantage of multiple clicks while at other parking companies, they normally just count 1 click only.