What are the requirements for obtaining a Thai tourist visa at the embassy in Vientiane?

You need a photocopy of your passport ID page and a photocopy of your entry stamp into Laos, as well as your passport photos. You can do these at the Thai consulate in Vientiane cheaply 5 baht each from memory. But if you're wanting to get a low number in the queue to give you an early pick up time the following day (important if you have a plane or a bus to catch back the same day as you collect your passport with your new visa in it) then if possible try to have all your photocopies done before you get to the consulate ie ask at your guesthouse or go to an internet cafe