I'm in the US and mainly use Patchwerks (Seattle-based) and Perfect Circuit. Patchwerks I find has a solid selection and great recommendations, service, and ship times. Perfect Circuit has a wider selection. On rare occassion I've bought from Detroit Modular and a shop in Oregon who's name I forget. All 4 of those have been worth going back to.

I buy most of my other stuff from Sweetwater, or less frequently, Vintage Audio King, but both SW and VK are much less knowledgeable in modular than those specialist retailers mentioned above. Hope this helps!