Are there any good sources available on reading funk guitar progressions and all about funk rhythm? I can play the rhythms well but I've never really understood them as much as I would like to so that I can easily improvise my own chord progs.

I searched on UG lessons section but only one article was there and it wasn't very clear.
You could check out musicradar.com


Although, not intended as a smart ass comment, but the best source that you're asking for will be your record collection, from which you should transcribe.

Some suggested listening would be Nile Rodgers, Michael Jackson, Tower of Power, RHCP.

You can only do so much with the classic dominant 9th shape and adding the 13th with your pinky, or m7 barre chord, but it'd be worth looking in to CAGED and triad inversion voicings on the top 3 or 4 strings.

Most funk is based off 16th note strumming, syncopation, and experimentation with where to place accents and muted notes.
Last edited by mdc at Nov 13, 2011,
The progressions in funk aren't really important.
The function of a guitarplayer in a funk band is to rhytmically fit into the band.
The most important shape would be an E9 shape.
Well I'm not sure about the E9 thing.
When I first started doing anything remotely funk, I started with "Earth, Wind And Fire" stuff. The chords are not tremendously difficult, but the picking hand is where the vibe is at and can be quite challenging. Check it out.
From what I've looked at I've seen 7, 9, #9 chords seem to crop up fairly often.