Luang Prabang is THE place to visit in Laos and is a wonderful little town full of temples and a great little night market where the people come down from the hills. We based ourselves there and went out to various places so I can't comment on the rest of the country other than to say Vientiane is a bit of a dead loss.
We were there some years ago when flying was a bit cross-your-fingers-and-hope-they-don't-crash, but it's (apparently) better these days and you can even fly direct from Chiang Mai: http://www.travelfish.org/feature/119
The alternative is to head along the Mekong to Nong Khai, cross the Mekong to Vientiane and then fly from there.
It's a great trip. Enjoy. over 9 years ago
i went from chiang mai to chiang rai then chiang sean and then over the border to huay xai in laos where you can get a boat down the mekong to luang prabang.. either slow boat (about 2 days) or fast boat (about 6 hours)... but that was a few years ago now - things are likely to have changed. there is nothing to see in huay xai, but it is a great place to be if you're heading north in laos... the gibbon experience that leaves from huay xai was one of the highlights of my trip in 2005.. http://www.gibbonexperience.org/ over 9 years ago