A good miniatures paint job can be ruined by bad basing; on the other hand, a miniature with an average paint job can really be enhanced by an inspired base. Here’s some advice on making scenic bases for your miniatures.
I’ve been impressed with the look of Sidney Roundwoods’ figures basing for some time. Now he’s done a tutorial on how he produces them.
The Mini Stories blog has a nice photo tutorial on making snow bases.
Here’s a tutorial on casting custom resin bases.