There are some great texture tutorials at GeekatPlay (http://geekatplay.com/index.php) plus they have some great beginners tutorials that will help you out.

For purchase, I highly recommend TerraPak (http://www.altuit.com/webs/hemingway/AltuitCover/default.htm).  These are materials that will not only look great, but help you create your own manterials once you read the included documentation. 

LVS - Where Learning is Fun!  
http://www.lvsonline.com/index.html