Fish Den is my lfs...definitely a trip back to the 80s, but a great place (that's 5 minutes from home for me)
On the weekends I sneak over to Neptunes in Highlands Ranch. It's a ways from Boulder, but a very nice shop for sure. Perhaps a smaller livestock selection, but I haven't seen an unhealthy fish there yet...and their selection of plants is better than any Denver area shop that I've found. Granted...I've only explored Denver / Aurora / Highlands Ranch...haven't made it up to Boulder yet.
hmmm...maybe I DO know what I'll be doing tomorrow afternoon, haha.