I dont know what you mean by "Funk at its core is dirty and noisy", if you mean the RHCP's style, then yes, I consider the RHCP's are more of a Punk Funk/Rap Rock band anyway.
Artist like Lenny Kravitz, Prince, & Maroon 5, just to name a few that are classified within the Funk Rock genre are not dirty and noisy sounding, dont get me wrong, the RHCP's have done alot in helping to bring the Funk Rock genre more mainstream and I am not trying to discount the RHCP's music, I am only trying to point out that most traditional (Funk) is not noisy and dirty sounding as suggested.
But then on the other hand, you have Jimi Hendrix, (whom most consider him as one of the main innovators of the Funk Rock genre), what I find when most people are discussing the subject of Funk Rock, they mainly describe the Funk part and say nothing about the Rock aspect of the genre itself, would'nt Rock be where the noisy and dirty sound originates more so than the Funk aspect. :)

Who do you consider the quintessential funk artists?

The Isley Brothers would have to be my favorite, and not only because they are from Cincy, Ohio.
They are my favorite combination of funk and electric guitar, these guys were ahead of there time in my opinion, of course they were rivals to Jimi Hendrix and influenced by Hendix's music also.
The Brothers Johnson is a favorite, some of the best (clean) funk bass guitar to this day.
I always liked the Ohio Players, Rick James, Commodores, Stevie Wonder, Prince, Sly & The Family Stone, Average White Band, Parliment/Funkadelic, James Brown, and Herbie Han**** had some good funk back in the day, although his music is mostly jazz orientated.
Most of my favorites are already imbeded here in the Soul & Funk forum, just scan through the threads.

And are those artists clean and generally well produced? Or do they have a certain "down and dirty" attitude towards their music?

I am mainly talking about sound/music, what does a down & dirty attitude have to do with funk music, and to answer your question, yes most of the artist mentioned are clean and well produced, espeacially the Brothers Johnson, I really dont understand why you insist that a down & dirty attitude is what defines funk music and artist more so than good dynamics and production . :confused: I admit there is a certain attitude that is associated with every genre of music, and I guess funk music would want a person to get down & dirty on the dance floor so you would be correct to a certain extent, it doesnt mean that funk music itself isnt well produced musically.

Yes, the Chili Peppers sped up the tempo and took the dirtiness to the extreme, but they still played plenty of pure funk, especially on Freaky Styley. They were white though, so I apologize for that if it looks goofy...

"dirty" to me means difficult to distinguish when talking about musical production. I think grunge is dirty. Funk is sometimes dorty, but the interplay of the rhtythm section, including guitars and keys, etc is usually well-defined, which is part of its appeal

Infectious Grooves FTW:

I beat you to the punch on one of the first pages haha, but yes excellent choice...