As of August 2015, there are now many international ATMs in Vientiane and one or more in most small towns in Laos. Bank branches are in provincial main towns. Several banks in the Lao PDR have ATMs which accept Visa, MasterCard, UnionPay etc. including ANZ Laos, JDB, BCEL (main Lao commercial bank), Phongsavanh, LDB and BFL. They all dispense Lao Kip only, have similar (local) transaction fees and there is a maximum daily limit per card across the network. Further details via the link below.

U.S. dollars (USD) or Thai baht (THB) bank notes are still accepted in most places, but it is best to change your money to local currency (LAK). Banks and money changers abound for changing both cash and traveler's checks and for credit card cash advances (expensive).

Do not rely on being able to pay bills with a card.  Where credit card facilities are available they usually charge 3-5% extra. Only the more expensive hotels and tourist restaurants offer credit or debit card payments.

You can get a whole lot of up-to-date info about Lao banks including daily exchange rates, accounts for foreigners, fixed deposit rates etc at Retire-Asia.com's Lao Banking page. It's a useful resource which is updated regularly.