The Photobucket site is a bit of a local Denver phenomenon. Started by Alex Welch who graduated from CSU at about the perfect time to launch a tech startup in Colorado. Photobucket is not nearly as well known among the tech crowd as Flickr and yet Photobucket beats Flickr in a variety of metrics (page visits, for example). Most folks in Denver have some connection to Photobucket through a friend-of-a-friend and people love swapping stories about how great and down-to-earth the guys are regardless of the amazing success of their company.
Slime Sandwich - Denver Game Company
Slime Sandwich is their next venture - an online, social, role playing game that will make money on subscriber fees. I found out about them because they kept coming up on the Colorado PHP News Aggregator that I set up - they're posting lots of jobs with a variety of skills. I created a channel for Slime Sandwich (which requires manual curation, but presents trend data that makes the manual activity worth it).
I look forward to watching the progress of slime sandwich over the next few years. According to a quick search they've got $1 million of seed funding on January 10th, though it's not 100% clear to me what the source of that funding was. They also can probably fund the company for a while based on profits that some of the founders made on previous projects. My guess is that it will take more than $1M to get their game online and start building the community for it so it will be interesting to see how they spend their money and build their business.