I don't live there anymore but I did for many years. Well, I never actually lived in Denver, but in Boulder. I can help you with some of this.
In Denver go to Wax Trax and its environs. There is cool stuff there. Also there is a good bookstore (Tattered Cover) and good record store (Twist and Shout) in the same building but the location is kind of dull. The other location of the Tattered Cover in Denver ("LoDo") is cool. The neighborhood across the river from there, near the REI is pretty okay.
Packrat antiques, for medical oddities. And there's some stuff near the capitol. Denver is full of dive bars but I don't know any of their names.
If you're mobile I'd check out New Belgium brewery in Fort Collins; they have a good tour. About 40 minutes north of Denver. And Oskar Blues, the people who do Dale's Pale Ale, have a food place in Lyon, about 20 minutes north of Boulder along a pretty road.
The area around Tennyson Street & 44 Ave is neat; a friend lives near there and is a fan of "Big Hoss BBQ." Oh and there's this place that sells burritos, weight-lifting equipment, and flower pots (last time I was there). I will try to find the name of this place for you. It was really really good.
Boulder is easier and I know it better. There are really only two areas, the Hill (you can avoid it) and downtown/Pearl Street. Stuff around there is pretty easy to find. if you continue east on Pearl street pass the pedestrian mall there are a number of good shops and restaurants. I would recommend going to Mountain Sun (or Southern which is in south Boulder). They have various hamburgers and beer. The Pearl Street mall has a very good toy store.
As for bars in Boulder, it's a college and rich town, so there are fancy places and total shitholes that are just shitty instead of dive-y.
Eat Breakfast at Lucile's in Boulder; it's just crazily fucking good. So good. I took some DC people there when I was in town for a conference and they couldn't believe it. Also the "North Boulder Cafe" is a bit out of the way, but worth going to. It is only open in the morning, then it turns into a Chinese restaurant. It is also very good and a good place to good Colorado-style green chile. (Green chile is mostly a New Mexico food but Colorado has its own variation on it.)
It's pretty easy to get to Rocky Mountain National park from Boulder. Worth doing.