As a local, I'll take a slightly different approach and recommend the places I think are making the best beers in the styles you said you are into instead of just the places I think are cool to visit or have the best overall beer selection.
For Pales and IPAs in Denver: Comerade Brewing and Station 26.
If you're willing to go just a little outside of Denver, I would recommend Odd 13 in Lafayette and Cannonball Creek in Golden. There's also Weldwerks, but they're way the hell up in Greeley. All of those places are doing great hop-forward beers right now. If you're into the current "northeast IPA" thing, Codename Superfan from Odd 13 is about as close as you're gonna get in Colorado. Honorable mentions for me in this category would be 4 Noses in Broomfield and Joyride in Edgewater.
For Stouts and Porters in Denver: Denver Beer Co makes a Graham Cracker Porter that people go Ga-Ga over. They also usually have a barrel aged version of it or two available at their tasting room. My favorite stout in Colorado is Left Hand Milk Stout(the regular version, not the Nitro), but they are in Longmont about 45 minutes north of Denver. Epic has a cool Denver tasting room and I like their dark beers. And there's always the various versions of Yeti from Great Divide.
Anyway, I hope that helps. And if you're looking for places with great tap lists where you can try lots of local beers, as others have already recommended, it's hard to beat Falling Rock Taphouse. Freshcraft is also cool.
Dan