Cliff was definitely a truly great bassist.
I'm not sure what kind of music you're into, but from guitarist to guitarist, I offer a short list of stuff that I hope will help you out.
Muse - Hysteria
- Not too terribly difficult, but sounds impressive and really helps with dexterity. Muse's songs are great for early-medium chops.
Communic - Under A Luminous Sky
- The driving basslines in this song are simply amazing. Erik shows his high caliber musicianship and writing ability throughout the entire album.
In Flames - F(R)IEND
- As In Flames is my absolute favorite band, I'm more than a little biased. Peter is an excellent bassist and his work more than deserves a good study.
Kamelot - The Human Stain
- Simply a great song. The basslines are intense and mesh beautifully. I haven't tried it yet, but it sounds like a fun piece.
Tool - Right In Two
- Tool is great for getting used to weird time signatures and simply badass (yes, it's both relatively simple and badass) fretwork. If you get into percussion, Danny is an excellent subject to study
Lamb of God - Descending
- This is just a beautiful, brutal piece. Somewhat fast.
KoRn - Blind
- Surprisingly simple, surprisingly fun to play along with.
Ultimate Guitar Tabs
-amazing site for tabs, chords, guitarpro tabs, and powertabs; updated daily
Definitely stick with it, dude. When I started out on guitar, I didn't have the benefit of a teacher and I was too retarded to try reading up on it, so I've been slow going. Five years later, I kept chugging along and guitar is one of the things that has kept me sane through high school and my first two years at university. It stays with you, and if you're lucky, it changes you in the best ways.
Well, there's my poorly written, barely edited $0.02 worth. I hope it helps, man. Best of luck to you.