Jazz Standard Backing tracks (completely free)
250 free backing tracks to most popular jazz standards. They are good quality, and keyboard-bass panned, so you can play along guitar, keys or bass by panning the backing track. Some are available in multiple BPM speeds. Excelent site!

Jazz "Vanilla Book"
Basic chord changes charts to many jazz standards

Backing Tracks for Guitar
Free Backing tracks arranged by artist. Looks like they have over 350 Artists and over 2500 backing tracks at the moment.

Wholenote.com
Features free guitar lessons with tablature and playback. OLGA tab search, composition tools, resources, accessory and sheet music reviews.

GuitarShredShow.com
A free Flash animated site where "Mr.Fastfinger" reveals the arts and secrets of heavy rock guitar to all.

BopLand.org
This site is a free knowledge database for improvising musicians, featuring hundreds of jazz licks over most common chord progressions.

EarPlane.com
A good ear training site. Teach yourself how all chords, scales, and intervals sound like. You can also work on developing a very fine sense of pitch by learning to hear the difference in cents. (100th of a semitone)

HarmonyCentral.com
This is THE site for music equipment reviews of any kind. Before buying that piece of equipment, first see what everyone is saying about it, so you don't waste your money.