This is a list of the many excellent sources of information about miniature painting I ran across. I sorted this list of links loosely by relevance. This order does represent my personal impression of the sites in question, and is by no means exact.
Hot Lead This website has some of the most detailed articles about basic and advanced painting techniques and special textures. Take a look at the gallery too.
Doctor Faust's Painting Clinic A nice set of painting articles with the most detailed study about removing paint I have ever seen.
The Miniature Collecting & Painting Center This website has very good introductory articles for the aspiring miniature painter and a beautiful gallery.
Imaginate This website has very good introductory articles for the aspiring miniature painters, covering all the basic topics. A nice place to start.
The Pewter Miniature Paint Shoppe Here you will find a good set of painting articles that have everything you will need to start the hobby of miniature painting.
Online Miniature Painting and Modelling Guide Here you will find some step by step painting guides and a lot of loose useful tips.
The most recent version of the Miniatures Painting Guide and FAQ is hosted here. Some more painting guides can be found here too. It has a lot of information and is worth a look.
Caution Wet Paint has some recommended articles about miniature painting.
Painting miniatures made easy - Mike Kan Paint This collection of painting tips has good descriptions of the basic techniques and painting guides for several Warhammer fantasy races.
Figure painting introduction by Solis Media This site has some really nice painting guides.
The Miniatures Page is one of the most useful source of information for the figure freak. It also has some painting guides.
The Virtual Alchemist has painting tips, hints about miniature photography and galleries.
Rob's Miniature Page Rob shows off his excellent paint jobs and has some painting tips too.
Larry Leadhead Get a deep (and funny) insight into the everyday life of a gamer.
www.thewarp.net is the new home of the paint pot. It also features news from the gaming scene and a sculpting guide.
Stan Johansen Miniatures has some sculpting information..
The Shaman's Miniature Hut This site has a good collection of articles for beginners.
Renaissance Ink sells stuff for painters and wargamers but also has some painting guides..
Minutiae: fantasy miniatures and scenery by Joel Patton Joel has written down some of his experience as a miniature painter in some nice short articles.
Scott's Web Pages have a neat introduction into miniature painting.
Lock'Mar has some workshop articles about painting and conversions. It also features an painting contest.
Zuiun's Miniatures Page This is basically a gallery but there are very instructive comments about the pictures too.
The Stuff of Legends This is not really a site with painting tips, but it is the largest collection of catalogues and lists of OOP miniatures around.
Gremlins in the Garage This site deals mostly with larger scale kits but has some relevant articles.
Gylas This site features a painting guide in italian language and galleries of course.
Vlad's Painting Pages feature a very brief painting article.
Cave of the Hellhounds This site is mainly devoted to tabletop gaming, but features a small section of painting tips.
Thomas Pope's Miniatures Page Thomas has some painting tips to share.
Boldo's Armory - Basics of Miniature Painting This page contains a short article about the very basics of miniature painting.
Miniature Web Planet This page contains some step-by-step guides on building scenic bases or small dioramas.
Medieval Armies DBA Page On this DBA page you will find some relevant articles, especially about the use of water-slide transfers.
Society of Ancients This website is mainly about playing ancient and medieval wargames with any set of rules, but it also has a small guide about basing figures. The most noteworthy about this site is the extremely funny "How not to" Guide to Painting and Model Making.
Squigger's Way Here the Squigger gives his opinion about how to paint horses, skeletons and orks.
Tastycow's W40K Stuff has some painting instructions for 40k figures.