the real basic map of vientianne, you will see Nokeo Khoumane street, there are some good guesthouses around. If I go I always stay in nr 16, Mixay guesthouse: serves free breakfast as well and free snacks and coffee all day long. Had a great experience with them a couple of times already, really friendly people and always ready to help you. Aircon rooms are mostly booked but you might check it out as the fan rooms are really ok as well.
around nr 17 are some nice hotels as well with good aircon rooms and really clean (also they have good accomodation provided for when you would like to go to Vang Vieng or Luang Prabang by mini bus instead of the main local bus)
There are various travel websites to research apart from this one re accom. and reviews eg travellerspoint.com; tripadvisor.com; virtualtourist.com. I will be in Vientiene next month and intend to stay at Wonderland 2 Guest House,next to That Dam,next to a bar called Blue Bananas,double,a/c,tv,fridge,$15/4-600B. I think this cost was in 2009. Only came across this GH through travel blogs and the reviews were very very positive. Good enough for me. My 2nd preference - Syri 2 GH.