Eminem's fifth studio album is tentatively set for release in the 4th quarter (winter) of 2008.  According to Ca$his, the album will be called King Mathers, but this hasn't been officially confirmed
He's a 35 year old white rapper, why you'd want such a date, is beyond me, but....
No official release date but here is all the info so far:
King Mathers is the tentative title for an upcoming album from American rapper Eminem and his fifth major label studio release.
50 Cent indicated that Eminem is preparing a new solo album. Labelmate Ca$his also attested to the new album, referring to it as King Mathers. He said that it would be released in 2007, and that Jay-Z would be featured on the album.
Eminem was in the studio with T.I. and produced three tracks, two of which were produced for T.I.'s album T.I. vs. T.I.P. (only one made the final cut) and one for Eminem. He’s back! After being away for three years Eminem is planning to make a comeback with King Mathers, his fifth solo effort in eight years. The album is currently slated for an October release, with it’s first single “Still Shady” hitting the air waves as early as mid-August. Two clips are scheduled to be shot in Los Angeles starting July 23rd, the first being “Still Shady” a track featuring a menacing guitar riff while Eminem attempts to reclaim the title he once was so modest of. The second clip to be shot, “Follow Me” features 50 Cent and has the duo flowing to a beat reminiscent of 50 Cent’s smash single “Out of Control” a track that will undoubtedly garner plenty of rump shaking in the club these up coming months. Long time friend and collaborator Jeff Bass claims, “Expect an album like you have never heard from Marshall. He’s been through a lot since Encore and has a lot to say. This album is very different from his previous work.” Bass also promised that fans won’t be disappointed by Slim Shady inspired tracks like “Still Shady” and “Never Gave A ****.” King Mathers also features a long overdue tribute to Mather’s fallen friend Deshaun Holton (Things Ain’t The Same), famous for his role in the film 8 Mile and a member of Mather’s Detroit rap collective D-12. You can expect King Mathers to hit stores October 16th. A special edition “King Mathers” will be released simultaneously featuring four tracks from the recently scrapped upcoming D-12 project that includes a surprising appearance by Three 6 Mafia as well as Stat Quo. “King Mathers” boasts possibly ten tracks produced by Dr. Dre as well as production from Hi-Tek, Dawaun Parker, Akon, & Eminem himself. The highly anticipated comeback album also features guest appearances by label mates Dr. Dre, 50 Cent, Ca$his & Obie Trice as well as Jay-Z, T.I. & Mary J. Blige.