I've made a few day trips to New Belgium and Odell, with a stop at Coopersmith's (pool, decent pub food) in Ft. Collins for lunch. A friend swears by Ft. Collins brewery, but they didn't have days/hours that matched the others. (And AB is on the way, but that was a wasted hour, even as far as a non-micro-enlightened friend was concerned).
Coors had a temp sign up a couple weeks ago that said no long tours for some reason or another, but the short tour is fun if you're in the area. Locals swear by Golden City brewery around the corner, and the crowds packing the patio could attest to that. But Golden does make a nice stop on the way to Boulder and Longmont, if that is your day trip plan. I've got a friend who has made the Avery/Oskar/Left Hand day trip a few times.
Ending up at Wynkoop or Coopersmiths to shoot pool is a decent evening with the guys, but you're limited 4 or 5 house beers, because they're always out of a couple. Agreed on Falling Rock if you've got friends who know their beer. Any of those three, and you've got the rest of the night for the LoDo club scene or Old Town Ft. Collins college scene, depending on your styles.
Strange Brewing and Dry Dock in Denver and Aurora are developing healthy crowds and have plenty of food/events for their fans, but I haven't made it to either, yet.