In addition to the ones suggested, there are two more I use on occasion....chorus and fuzz.

I don't use chorus as often as I used to, but when I need it, it's just what the doctor ordered. Though I don't use it often, I wouldnt' want to be without it. For the typical jangly chorusy sound, think Pretenders.

Fuzz I could honestly live without, but some cover songs I do require it.

I was in the dilema of what pedals to get a few years ago. I ended up getting a multi-effects unit since it cost less that the pedals I wanted. My first MFX unit was a Zoom G5. Currently I'm using a Boss GT-100. The original intent was to experiment with the various pedals and see what I wanted to get. Now I just use the MFX unit..works for me.