http://www.musictheory.net/
This is a GREAT site! You may not be into music theory but it's the building blocks of music. This site is great for all aspects of music! Ear training, note recognition, interval training, etc. This isn't the flashiest site but its very helpful.
http://www.youtube.com/user/Guitartricks#p/u/22/pNzJmURoPuQ
I just found this site not long ago. It's great!!! They have all sorts of guitar lessons on their normal site and some free lessons on their youtube site. Check it out!
http://www.guitarinstructor.com/
This site is cool too! They have online lessons that you can view for only $1.99 per lesson. Not a bad price! There is a wide variety of lessons from professional players. They have lessons ranging from rock, jazz, blues, to even guitar maintenance.
http://www.harmonycentral.com/index.jspa
Harmony Central is a invaluable website. There are all kinds of user reviews on amps, effects, guitars and anything else that deals with music! If you're thinking about buying some gear check this site out first to see what others think of it!
http://brokenheadstock.com/
I also follow a few different blogs. This guy has a great blog! I found his blog one day after searching for a tap tempo pedal schematic. Check it out http://brokenheadstock.com/?p=82 . He discusses his gear and what's worked for him.
http://godgearandguitars.blogspot.com/
This is Chris Lockwood's blog, he's the guitarist from the band "33 miles". I love the name of his blog, God, Gear, and Guitars! They have some great songs too!
Ok so there are just a few websites that are very useful. What about you? What sites / blogs do you follow? List them below!