Riga Old Town Hostel is right in the old town and just two minutes from the bus station. +371-7223406
Friendly Fun Franks is famous for that you get a cold beer as first as you enter the place. Novembra Krastmala 29, +371-25990612, friendlyfun@franks.lv, online booking.
If you need a map of Riga take Mr Gordonsky's CitySpy Map. It also contains useful informations of things to do. Another good source of information is Riga In Your Pocket. You can also have a look at the official Riga Tourist Information or Latvia Tourist Information.