Arvada/wheat ridge - west side of town, slightly more expensive than average metro prices, good investment, in my opinion
Aurora - east side of town, cheap, murder capital of colorado, bad investment
Boulder - if expensive houses and pompous people are to you liking, boulder is for you. Good investment, though
Broomfield - north side of town, moderate prices, decent investment
Lakewood/golden - west side, moderate prices, good investment
Northglenn/thornton - north side, cheap, mediocre investment
Littleton - south side, moderate prices, decent investment
Denver proper - large variety, depends on area
Highland Ranch - south side, overbuilt, bad investment
Louisville/superior - west side by boulder, moderate to high prices, decent investment
Longmont - probably worth looking at, 30 minutes from the edge of town, higher prices, mediocre investment(also overbuilt), I used to live there. It seems more relaxed than the denver area.
Brighton, strasburg, other areas east of town - cheap and overbuilt, long trip to mountains