Vientiane is small enough in that it is fairly easy to walk around looking for lodging (if you do not have pre-arranged accommodations).
Tuk-tuk drivers are found all over town – and for a few thousand kip will take you across town. Be sure to bargain with these drivers – in my experience they always initially offer a very high price.
Hayasoke Guest House is a clean, comfortable, & affordable guest house located at 083/1-2 Hengboon St – several blocks in from the Mekong River. Its within walking distance of the river front, Internet cafes, and the main center of town. There is a room on the ground floor (3 beds) – and of course more rooms on the upper floors. For more information please visit email them at firstname.lastname@example.org or visit: http://haysok.laopdr.com/
River View Hotel is about $15 a night for singles – ask for a room with a view of the Mekong – as a lot of the rooms here do not have views. For more information call 216244.