Boulder is more startupy and small to medium size companies, but just southwest of Boulder is Interlocken, which has some biggish tech companies (Oracle and Level3 being the largest). Downtown Denver has all manners of software companies, from startups to big telcos. And then in south Denver (about 1-1.5 hours of commuting from Boulder) are a bunch of larger corporations (it's called the Denver Tech Center).
I've gone from lusting over migrating my career to the Bay Area, to becoming almost completely averse to the idea over the last two years.