Just to clarify, Black Butte is a porter, not an IPA. We served that at my wedding.
The classic Fuller's London Porter is still the best porter IMO, but one of my favorite beers of all time is the Rogue Mocha Porter. I also recommend the Anchor Porter.
IPA lovers, make sure you check out AleSmith IPA (if you can find it) and Stone IPA, both from the San Diego area. For imperial IPA (also called double IPA), I recommend Dogfish Head 90-minute, Speakeasy Double Daddy, and AleSmith Yulesmith.
My favorite Belhaven is the Wee Heavy. If you haven't tried it, do your best to find it. The Scottish Ale and St. Andrews are also very good. If you like the Scottish-style ale, McEwans is a nice alternative to Belhaven.