as noted at 3 miles almost anything, but you might get hooked so think beyond just the 3 mile commute

lots of good shops in the area

My favorite is Willow glen bikes (not the cheapest but great service)

but you have also have REI, the off ramp (santa clara), wheelaway, hylands for starters

and for used

from craigslist a sampling of whats out there used

http://sfbay.craigslist.org/sby/bik/2446866738.html

http://sfbay.craigslist.org/sby/bik/2446270579.html

http://sfbay.craigslist.org/sby/bik/2446219729.html