Get in Laos
Russians, Korean, Japanese, Swiss and ASEAN nationals including Indonesia, Malaysia, Singapore and Philippines can enter Laos "visa free" immigration web; all other tourists need a visa in the form of a tourist visa (for one or possibly two months) issued by a Lao embassy or consulate. A visa on arrival isalso available to most people entering at the airports in Vientiane, Luang Prabang and Pakse, as well as the Thai-Lao Friendship Bridge between Nong Khai in Thailand and Vientiane and on the Lao/vietnam-Border. It is also available when entering via Stung Treng (Cambodia), although guesthouses in Cambodia and the Lao embassy in Phnom Phen will tell it is not to make money with visa services. When applying for a tourist visa or to obtain a visa on arrival, one (maybe two at Lao embassies) passport photo is required (although you may be able to pay a US$1 "fee" to have this requirement waived).
Prices range from US$30 to US$42 depending on nationality - Americans US$35, Canadians US$42, Australians US$30, Chileans US$30, Belgians US$30, British, Dutch, Italians US$35, Swedes US$31, Germans $30-$35.
Visas can be obtained in advance from Lao embassies/consulates. The fee varies by nationality/embassy; US$20 is common, although can be as high as US$63 (in Kuala Lumpur). Processing times also vary; 2-3 days is typical, though you may be able to pay an extra small amount (around US$5) to receive the visa in as little as one hour. In Phnom Penh the travel agencies can arrange the visa the same day (but may charge as much as US$58) while getting it from the embassy takes a few days. Getting a visa from the embassy in Bangkok costs around 1,400 baht for most nationalities, plus 200 baht more for "same day" processing. It's cheaper and quicker to get one at the border.
Visas are also available at the Lao PDR consulate in Khon Kaen, Thailand. Thai and English (limited) are spoken by consular staff. Hours are Monday-Friday 08:00 to 12:00 and 13:00 to 16:00. (UPDATE July 2012): There have been several changes that took place in February 2012. Prices have increased and are now similar to those charged by the Laotian Embassy in Bangkok.
Visas for Americans, Britons, and those from several EU countries cost 1,400 baht/US$45, Australians and New Zealanders pay 1,200 baht/US$38, Canadians pay 1700 baht/US$54 while Chinese pay 600 baht/US$20. Officially, visas can be picked up the next day (or pay an additional 200 baht to have the visa issued within 1 hour). Officially, only baht is accepted. However if you don't have baht may take US dollars. Note: When asked, consular staff were using a 30-31 baht to the dollar rate, making it more expensive than getting one on arrival and paying in US dollars). Given that a visa for many countries can be had for US$20-42 at the border, getting a visa at the border is cheaper and quicker. NOTE: If you are taking the direct Khon Kaen to Vientiane bus and you require a visa for Laos, the bus company will not sell you a ticket unless you have a visa already issued.
There are visa-on-arrival facilities at the international airports in Vientiane, Luang Prabang and Pakse, and at all border crossings (see below), including now overland from Cambodia (visa on arrival facilities opened at Voen Kham -north of Stung Treng, Cambodia). The cost varies between US$30 and US$42 (if paid with US$ notes; paying with Thai baht will cost considerably more and border officials will not accept Lao kip at all). If you pay in Thai baht, the cost is usually 1,500 baht (about US$47-48). A US$1 "out of office hours/overtime" surcharge, and a small (possibly 10 baht to US$1) entry stamp fee, might also be charged.
Entry permit extensions (sometimes referred to as "visa extensions") are available from the Immigration Department in Vientiane, the Immigration Department in Luang Prabang, the Police Station in Pakse, the Police Station opposite the Lao-Mongolian Hospital in Phonsavan and possibly other cities. Extensions are not possible in Lao's second city, Savannakhet, although you can do a border run from there to Thailand to get a new 30 day visa. The cost is US$2 per day plus a small "form fee" ranging between 5,000 kip (Pakse) to US$2 (Luang Prabang.) The process is very easy; turn up in the morning with your passport and one photo; fill in a form (in Luang Prabang immigration officers do this for you) and come back in the afternoon for your extension.
If you want to extend for longer than two weeks and are near the Thai border, it can be more cost effective to cross the border (entry to Thailand is free for most western nationalities) and return immediately to get a new 30 day Lao visa.
Extensions are also possible via agencies elsewhere in Laos (who will courier your passport to Vientiane and back again, around US$3 per day minimum of 7 days).