the pedals I want to own and can actually see myself using are
chorus (i use this alot! but the line 6 spider II has a built in chorus, so a chorus pedal isn't an immediate need)
distortion (yes, I play alot of hard rock and metal so this is mandatory, and yes I feel as though my amps distortion is not sufficient, and I don't like most of the distorted amp models on my korg pedal)
overdrive (for use as a booster and a stand-alone pedal, I didn't know the difference between distortion and overdrive until recently, then I actually decided to listen to some sound clips of some overdrive pedals and I love the tone! so an overdrive is a must!)
wah (can't see myself using it often, but my korg pedal has a built in wah, it sounds terrible, but it's so much fun to use when goofing off at home, so, not too high on the prioritys list)
delay (I love putting a short echo onto a solo so it sounds almost like you have 2 guitars playing the same thing at the same time, I love it. my amp has a "tape echo" which I don't like, and a "sweep echo" which I don't like either. preferably a pedal that can do both reverbs and delays or echos)
compressor (mainly for recording, and I rarely record, so it's not high on the prioritys either)

and that's pretty much it... so, to recap that's chorus, distortion, overdrive, wah, compressor, and a delay/reverb (though it's more important that it has delay then reverb)