Part of my previous recommendation stands: it's hard to go wrong with a good overdrive (a TS-9, a BOSS Blues Driver) and a chorus as a starting point. You'll be able to get so many good tones from that combo, and you don't need an effects in/out in your amp (since they should be "in front" of that signal anyway). Wah-wah, too.
Again, if you're looking for more unique tones, any DigiTech Whammy product is going to get you that harmony/pitch shift thing. A synth pedal will do some odd things to your guitar's sound. Flanger can be made to APPROXIMATE a chorus at times, but it's more metallic and "swooshy." And if you're ever looking for "funk tones," get a Phaser (lots of Parliment/Funkadelic has phaser on it, but you can also do plenty of other sounds with it -- for example, the solo on No Doubt's "Just a Girl" sounds killer with some phaser).
If your amp doesn't have any reverb built-in, you would probably want a hint of it in your chain. Lots of guys swear by Delay, but TBH it's never been my thing as much as the other modulation pedals/effects (Phaser, Flanger) have been.
And if you want to get really nuts, check out a Tremolo pedal. It goes from a subtle warble to a very clipped "on/off" or "high/low" effect that can be quite useful.
Then... chain them together. You can get weird combos putting pedals in the "wrong" spots in your effects chain.