Theres a lot of high ranking groups that I've hardly ever even heard about, so if you guys have any post them here.

19. Radiohead
27. The Smiths
33. The Kinks
42. Roxy Music
44. Pixies
48. Sonic Youth
49. Blur

Ones I'm interested in exploring:

10 Jimi Hendrix (I've got his first 3, but don't know them well)
14 Marvin Gaye (only have What's Going On)
16 The Clash (love London Calling but don't know much else)
19 Radiohead (haven't heard much)
23 Elvis Costello (haven't heard much)
26 Talking Heads (I love Speaking in Tongues and enjoy Remain in Light, but don't know much else)
32 James Brown (only know the main singles)
33 The Kinks (only know the main singles)
39 Otis Redding (I've got a great compilation of his, but want to explore his output a bit more)
50 Ramones (I have their first 3 albums, but don't know much else)

wow you guys put radiohead in!
I can honestly say that you MUST try and listen to radiohead pronto!
They IMO have defined this generation of music, and lead the pack in terms of creativity, originality and brilliance. However don't start with Kid A or Amnesiac (amazing albums) as it may be a little much for the start. I recommend the bends as a starting point.
Anyhoo bands I wanna know more about are Joy Division and New order, slowly but surely I am listening and appriciating the music, but would love to know more!

New Order and Joy Division are well worth the effort, I think! I have a CDR of OK Computer somewhere. I think my wife has The Bends...

In the top 50 nobody, in the top 100 I'm checking out PJ Harvey and Nick Drake at the moment.

I also noticed the Kinks on the first two lists. For years and years I was only familiar with the hits, which I liked OK. But over the last few years I've really been enjoying their late 60's, early 70's album material. It's different and better than the popular stuff. Face to Face (1966), Something Else (1967), Village Green Preservation Society (1968), Arthur (1969), Lola vs. The Powerman (1970), and Muswell Hillbillies (1971) are all great. I think they hold up today a lot better than most stuff produced during the same era. I would start with VGPS. The Kinks music from this era is smart, funny, and catchy--everything you could want from pop music. Well, I guess it's not great dance music, but other than that. Check it out! Plea over.

My list:

David Bowie (I have some of the albums and have heard most of the songs, but never gave it the sort of study merited of the 4th ranked artist).

Van Morrison (I don't have any of his albums, but have nothing against him).

Blur (I like "Country House" but I don't know much about this band. The 1990's are the decade that got away from me, musically.)

25. Aretha Franklin
32. James Brown
39. Otis Redding
40. Sly and the Family Stone
43. Johnny Cash

Most of my focus in music since I broke out of just mainstream has been on albums, so I haven't gone very deep in the catalogs for a lot of the pre-album greats.

Sly and the Family Stone is only there because I keep seeing one album of theirs high on lists and I've never heard it, I've only heard Stand.