You should also consider using
HOSTELS while in Riga.

They are great places to meet other travellers and make some new friends. Especially if you are travelling solo. Much more social then hotels and way more friendly! you can use major booking sites such as hostelworld.com and hostelbookers.com. Then simply search latvia and riga and you will get around 25 options for hostels in Riga!
These sites also offer customer reviews and ratings of each hostel. So you can find much information about the place before you visit and also photos...
Whenever I travel I use these sites... so much better then using hotels!
You can actually do you research using these sites... but when you make your decision you should try and find that hostels direct website rather then booking through the booking engines!
Doing this simply means the hostel gain an extra 10% rather then that money going to the booking engines (like HW or HB).