Flying Dog Gonzo and Ballast Victory at Sea are my two favorites. The Polish porters are also excellent, as the above post states.
It's a damn shame that we're on page 2 and no one has mentioned Samuel Smith's Taddy Porter. My two other favorites are easily Founders' and Smuttynose Robust Power. GL Edmund Fitzgerald and Deschutes Black Butte, though I've only had each once, are both fantastic. Boulevard's Bully! Power is pretty good, but I would stay away from Maine Beer Co's King Titus. MBC makes great (if overpriced) beer, but King Titus tasted like cigarette ash.
I'm a big Porter guy as well; the first ones that come to mind (in order) are London Porter, Black Butte, Founders, Anchor and Sam Smith's Taddy Porter. London Porter has always been one of my favorite beers
My three favourite porters are Eddy Fitz, Founders and Black Butte but a couple that rival them include O'Dell's Cutthroat and Tyranena's Coffee Porter. The former is very much akin the easily sessionable ones that make up my faves and the latter is quite similar Founder's Breakfast Stout, imo. Every bit as good, too (I may be suffering from FBS overkill). Also, although the reviews don't treat it as kindly, I really liked Ass Kisser's porter as well. Samuel Smith's Taddy porter is also phenomenal. If you like porters, you'll probably dig Surly Bender, a very rich brown ale that also has a coffee version.
And then come up with your own personal explanation of what characteristics distinguish porters from stouts, based entirely upon your own experience. Better yet, pick up some Anchor or, if accessible, Mayflower.
I don't have anything new to provide, but here is another vote for either Anchor Porter, Deschutes Black Butte Porter, Samuel Smith's Famous Taddy Porter, or Smuttynose Robust Porter.
Stone smoked porter w/vanilla beans. Awesome. I didn't try the one with chiles in it, but heard it was good. I'll second Black Butte and the imperial version of blacke butte every year is amazing.
Morke Pumpernickel Porter. It's a Norwegian (I think, maybe Swedish) porter that's very good and a bit under rated.
Ed Fitzgerald is amazing. Smuttynose Robust Porter is excellent as is Black Butte. SN Porter is very solid and inexpensive.
Some of my favorites: Smuttynose Robust Porter Mayflower Porter CCB Jose Marti Meantime Coffee Porter NEBCO Ghost Pigeon Porter
Not sure if you're in the New ENgland area, but if so be sure to grab six pack of Mayflower Porter. It's the best Porter I have ever had. Also from New England is Smuttynose Robust Porter and Long Trail Coffee Porter. All three of those beers kick mega ass. As for widely distributed....if you can get Founder Porter is excellent (I'd put it right behind Mayflower's on my list). Also, Sierra Nevada makes a good porter.
Can't go wrong with Stone Smoked Porter! pretty tasty and only like 3$ And easily obtained. And the one with vanilla is extra awesome!
Boulevard Bully! Porter, Sam Smith's Taddy Porter, and Anchor Porter are wonderful representatives of the style.
Yes let's not forgot about our overseas brethren. Samuel Smith's Famous Taddy Porter is as good as any, and it should be readily available.
Arcadia's London Porter, then Smuttynose's Robust Porter, then Bell's or Founders. If you want a real treat then take a step up to Arcadia's Shipwreck Porter, it's bourbon barrel aged.
I'll also throw Mayflower Porter out there. The distribution is limited, but if you're in MA or the New England area, its definitely a must try and maybe the best beer they make. And like others have said previously, Founders Porter is top notch.
Founder's Porter might be one of my favorites, but I also second the recommendations for Smuttynose Robust Porter and the Mayflower Porter. I also enjoyed Anchor Porter.
I forgot about Arcadia London Porter. Great brew. I should do a side-by-side in the near future. It's funny because I considered porters to be one of my least favorite styles for a long time. To me they tasted like overly carbonated stouts or burnt watery lagers. Then I had my Founders porter and it ironically became one of my favorite beers, in the always accessible category at least. Baltic porters and Arcadia followed. Now I seek out porters. That's one of the best parts about craft beer, just when you think you have a developed opinion, it can be turned upside down by a great drink at the right time.
Revolution's Eugene porter is one of my favorite beers during winter. I second (third, tenth, whatever) trying Smuttynose Robust Porter and Founder's. I also really liked Slumbrew Porter Square Porter out of Massachusetts, but I brought this back from vacation and haven't seen it anywhere around Chicago.
Other than the more framiliar ones already mentioned, these are very memorable porters in my book: Harviestoun: Old Engine Oil Marshall Brewing: Big Jamoke
If you are ever in Colorado, Odell Cutthroat. I always like Stone Smoked Porter. There is really not much smoke taste. Not sure wher you live,but my local porter is Sweetwater Exodus, very solid.
Smuttynose Robust Porter & Deschutes Black Butte are exceptional! If your looking for a bigger Porter, I'd say Williamsburg Alewerks Bourbon Barrel Porter &/or Alaskan Smoked Porter. Either one of those are world class for what they are. Shit, even everyday Porters such as Anchor Porter, Sierra Nevada Porter, and Fullers London Porter are world class imo.
If you like coffee, go for the Berkshire coffeehouse or Kona Pipeline...both fairly easy to get and for a low cost. Also, we just got a HUGE shipment of Black Butte XXIV Anniversary in Arizona a few weeks back (which I'm sure someone mentioned on top of regular BB), so try and get a bottle or two of this as well...it's wonderful.