I have currently been playing for 7 years at this point in my life and have learned a lot over the past couple years at college, but I can honestly say that I would not be even half as good at playing guitar if it wasn't for some of these sites. Don't just look at these sites as links. These links are vital tools to becoming a better guitar player, and heres why....
This site is truly a plethora for the growing guitarist complete with lessons, forums, product reviews, an online composer, and my most personal favorite the "Grove Builder" With the Grove Builder you can set up and play chord progressions that loop in order to practice soloing or drill a tedious melody line. And if you're a Bass Guitar Player check out Activebass.com
While Wholenote.com has just about all the resources one could think of, if your specifically looking to learn a new technique or skill on the guitar such as mastering modes, scales, tapping, chordal structure, sweep picking, or tremolo picking then Cyberfret.com is the place to be. Cyberfret.com has some of the most professional, but easy to understand lessons I remember when starting out. It is perfect for the beginning guitarist.
Looknohands.com - Chord House is an absolute must if you need to learn how to play a new scale up and down the neck. It has every scale, chord, and alternate tuning imaginable for guitar as well as a section for piano chords and scales.
When I just starting out(and guitar tabs weren't illegal), Musician Forums was a sub project of Mxtabs.net.... Now however it is Sputnickmusic.com which is a massive music review site. Personally I think that these forums have the most knowledgeable musicians to ask questions or search for answers out of any of the links listed here.
5. Virtual Playground
If you need drum loops this site is a must. I mean seriously check it out, how much more could you ask for?!? It has tons of drum machine emulators from the 70s-90s. If you need more, go out and buy one :P
Arguably the best guitar tablature software ever invented. And it just keeps getting better. With Guitar Pro 5 it now has a "Realistic Sound Engine" you have to hear to believe.... This isn't just some crappy midi creation program. It blows all others out of the water because it actually sounds real. What CGI has done for animation Guitar Pro does for Music.
Ever want to learn everything you could about classical guitar? Now you can and all in one convenient package.
8. Harmony Central
Now Harmony Central is a huge resource one could go on for hours about, but I would like to focus on their guitar software section. If your a serious guitar player you can seriously benefit from some of the amazing software that is out there nowadays, some of which is free. Check it out!!!
Much like Classic-guitar.com was for classical Jazzguitar.be is a jazz information rich website. Just do it already :)
10. Google.com(Specifically their pdf search)
WAIT!!!!! Now I know what you're thinking I got lazy on number 10 and used a cop out. Not True!!! Here's the deal I'm not talking about just searching google like you might do every day. I'm talking about using the "filetype:pdf" in front of a search query like "jazz" to come up with a result such as an ebook on Jazz Scale Theory. I'm not kidding you really can find useful guitar ebooks out there on guitar. Just try it, click the link and change the word guitar to whatever you want to search for!
Well That's The List! Be Sure to Drop Me a Comment with Your Favorites!