My favourite riding partner is my friend Dave. We ride when we can during summer and winter. He even conformed me into buying a hybrid (which I bought today). I'll finally be able to match his top cruising speed.
Of course my girlfriend is a close second. I bought her her first bicycle a few weeks ago as her birthday present. She loves it but insists on riding late at night because there's less traffic then. I give her a year and she'll be tearing around the city with the best of them.