Loveland, Longmong and Niwot are all relatively close, and have similar quality of life properties, but are quite a lot cheaper--they don't have the university, which can be a bug or a feature depending on your perspective.
Fort Collins is another university town but with a lower national profile than Boulder, which again can be a good or bad thing.
+1 on Fort Collins - relocated here five years ago. It's a fantastic town - many big city amenities for a small city. (For example: it has a ton of restaurants. I used to live in NYC, and many places in Fort Collins are comparable in quality.) Cost of living in town and in the surrounding area is very reasonable, and quality of life is great.
Mountain views everywhere - the whole town is only a few miles from the mountains, similar to Boulder. Tons of parks, trails, mountain biking, etc. The city is very bike-friendly. Whitewater rafting is also close by on the Cache La Poudre River, which exits the mountains ~10 miles NW of the city. Public access boating available on Horsetooth Reservoir.
Also there's a lot of stuff in Erie and Lafayette which are both fairly close and less expensive. In a Zillow search I found some 4 bedroom houses in Lafayette with an acre in the $400k region, a 20 min drive from being in town.
Fort Collins is another university town but with a lower national profile than Boulder, which again can be a good or bad thing.