Sega is releasing a PS2 compilation of the Wonder Boy series, in Japan only. I'd grab that for sure if it came out here -- especially since you get to play the different versions of the games (the SMS Wonder Boy is too easy? Go for the Mark III version, which is identical, but with wasps from the very start!).
Here's some info on it, if you have a modded PS2 that can play Japanese imports: http://www.ncsx.com/2007/030507/monster_world.htm
It sells for $29 US on both NCSX and Play-Asia.