Below is a list of sites which I believe are well worth checking out. All are extremely informative with some stunning work featured and all are updated regularly.

If you'd like to exchange links feel free to email me.

A link to 'WarPaint Studio' a site dedicated to painted miniatures by David Gulczynski, 3rd place winner of the Reaper Online Painting Contest and a damn fine painter. Lots of very well painted miniatures to see here.
A fine site by Patrick Gordon, dedicated to painted miniatures and finely crafted terrain. Contains a large and especially impressive gallery of 40K miniatures.
Inspirational site by the one and only Dirk Stiller. You'll see some of the best work around here and not just in the usual genres either. Some brilliant, larger scale horror movie figures will be found as well as plenty of Sci-Fi and Fantasy.
This is a site by Holger Schmidt featuring many very nicely painted miniatures and other resources of particular interest to German Gamers.
This is a site which showcases the work of two brilliant painters, Garrick and John. Garricks work is some of the slickest I've seen, if you're having trouble with colour-choice Garrick's work will surely inspire you.
A site by Craig Stocks, I hope Craig doesn't mind me saying this, Slapping Paint is one of the few sites where you'll be able to see a very visible improvement in the quality with each passing mini. Keep an eye on this site, I think Craig will be one of the best painters around pretty damn soon.