dude, this can usually be answered by one simple question..."what kind of pedals do you want on your pedal board?"

I'd go with:
a distortion of your choice
a wah of your choice
an overdrive, of your choice
a chorus of your choice
a compressor of your choice
and a delay of your choice

also, maybe look into a flanger, and a phaser...but its really all up to you...you cun cut down costs by getting something like a Pod Xtlive, but that has amp models on it aswell...if you dont want multi-effects, then just get a few analog stomp boxes...whichever ones make the noises you wanna make