List it on sedo.com and see if anyone bites.
I sold a four letter .com few months ago for $1,500, but ICANN opening up the TLD space crushed the valuations. Unless you own a typo of a frequented website (the goggle.com guy is doing good) or have luck as cybersqutter (adaware.com owner used to make $20K/day doing nothing) you will not have easy time monetizing it.