If you’re interested in high-end coffee, Giv is good as a few others have mentioned. I’m not sure if it’s still the case, but their beans at least used to be available to buy from the Jitter Bus and Pistachio. Fussy and the Coffee Pedaler often have some nice high end beans for sale. Atticus Market sells Ilse, which is very expensive but very good. I’ve also occasionally seen a few other high end roasters at Atticus.

If you’re willing to drive a bit out of New Haven, Neat in Darien has excellent beans and is a very nice cafe, Roanjena in Glastonbury has Giv and often Ilse and is all-around an excellent place with great coffee and awesome baked goods, and Source Coffeehouse in Bridgeport has Passenger (PA based) and a rotating guest roaster, sometimes a local roaster.

I personally think Willoughby’s is dreadful, but if you’re into dark/medium roasts, they’ll probably have more of that then the other places I mentioned.