Housing close to campus is quite abundant, but sometimes pricey. The campus-run married student housing complexes are both close and reasonably priced. If you have small children, they are very attractive. The area called the Hill west of campus is a bit of an undergrad ghetto (noisy, lots of parties, crowded quarters).
The bus system is quite good and a bus pass is often included in the student fees, so students ride for "free". It runs all over town and to the surrounding towns of Longmont, Louisville, and Lafayette. Housing outside of Boulder is often less expensive and offers more space. The bicycle is the vehicle of choice among students; Boulder is compact, flat, seldom rainy or snowy, and has lots of bike paths.