Alimination
Space Adventurer
One of my main sources of synth sounds (other than individual pedals) is the Line 6 M series. I have both an M13 and an M9. Synth sounds, reverb/delay combos for ambient sounds (even all effect units being set to the same delay or reverb), built-in looper, either one is an amazing Swiss Army knife of sounds. (I'm partial to swell delay/ducking reverb, for that ambient "Space Station" sound.) Dig through the various M13/M9 and even the HD500/400/300 vids on YouTube for examples of the effects being used for non-obvious sounds.
I use a variety of multi-FX units for synth sounds, but I figured that the Boss GT-10 might be overkill for your purposes, the ME50B might be too big, and the Korg PX5D might be too small.
I like multi-FX units because they let me have the equivalent of my huge "modular synth" pedalboard in a smaller space. For inspiration, I suggest you watch/listen to the various Electro-Harmonix "Effectology" videos, and then figure out what pedals you can substitute for the specific EHX ones used in the video.
Good luck!