After the initial post on this topic there remain a few sets that were left off. So here we go...
The Funk Box 2000- Here's another fine piece of work from Hip-O Records. Covering 1970-1982, this four-disc set hits most of the high points from funk's golden era. James Brown, The Meters, Ohio Players, Funkadelic, Brothers Johnson, Rick James, Bootsy Collins, they're all here. The selections are mostly dance floor hits, and there's always room for debate over what isn't included on a set like this, but this one's pretty solid, and nicely varied. It includes a number of artists not immediately associated with funk (O'Jays, Curtis Mayfield, Marvin Gaye, Aretha Franklin), as well as the most obvious suspects (Brown, Kool & The Gang, Ohio Players, Rufus, George Clinton) and quite a few bands you may be hard pressed to remember (The New Birth, Jimmy Castor Bunch, Brass Construction, Bohannon). The selections are consistently good, and the definition of funk is broad enough that the set is varied and eclectic. It's too much funk for many, but it is an excellent overview of the best of the genre. Do it 'till you're satisfied.
What It Is! Funky Soul And Rare Grooves 2006 Here's a set from Rhino Records that is a lot of fun but does not maintain their usual high quality. The tracks are from 1967-1977, and most of the big hits are missing on purpose. Focusing intentionally on lesser-known artists in an attempt to show that there was a lot more funk happening than just the artists on the Funk Box, this is "dirty, gritty, gutbucket funk" according to the excellent book that accompanies the set. Mixed in with a few name artists are many groups distributed by tiny labels and the occasional one almost-hit wonder. As an historical study in funky soul, it is a worthy complement to the big stars, but you've got to want it bad. Compared to most Rhino box sets, the lesser-known artists often sound like they were lesser-known for good reason. There's plenty of good stuff, but those tracks would have fit onto two discs.
Atlantic Soul 1959-1975 2007 Atlantic was a hotbed of great soul stars in the sixties, and this set is packed with great performances. Aretha Franklin, Wilson Pickett, Solomon Burke, and Patti LaBelle are mixed in with many lesser-knowns, and the quality is quite good. Hits from the smaller artists, and less well-known songs from the big stars help to make the set something other than just another soul compilation with the same old songs. With only Atlantic artists represented, it can't be the set that Rhino's Beg, Scream and Shout is, but it's a good look at a label that did a good job with a variety of soul sounds. You have to be open to hearing some songs you missed the first time around, so don't come here for a comprehensive soul hits package.
Well, I think that mostly covers my collection of R&B box sets. There are of course lots of single and double disc compilations for the more casual fan, and I've got some of those, too. Let me know if I can help you find the set for you.