There are plenty great funk bands and guitarists.
When I listened to funk James Brown, Tower of Power, Mother's Finest and Marco Parker (sax player) were the acts to follow.
A favourite funk guitarist though is Keziah Jones, who describes his music as Blufunk (which is a fact), perhaps not classic hardcore funk, but great funk-fueled music IMHO.
I loved the two first albums of his (Blufunk Is A Fact and African Spacecraft) but didn't follow him after that, as I focused my attention on other music styles.
Keziah Jones - Wikipedia, the free encyclopedia
Rumors at the time had it that he turned down a spot as a guitarist and back up singer for Michael Jackson to pursue a record deal for his own music - don't know if that's true.
I consider Nile Rodgers a class A funks guitarist, listen to his work with Chic Le Freak, some might say it's disco, but to me he is applying funk to disco.
Apart from Keziah the only bands from that time that I'll sometimes listen to today is Mother's Finest (get the Baby Love Live album from 1979) and the now defunct band Defunkt, classic funk mixed with rock guitar sound. Back in the day I loved their Cum Funky album.
This is just a few quick ones of the top of my mind, I'm sure others will list a few where I'll think to myself, how could I forget to mention them. Truth be told it's been a long time since I listened to a lot of funk.