On SACD, the choices are Kubelik (on Audite--haven't heard it), Nagano (got bad reviews), Colin Davis (ditto), and Haitink (1971 4.0 SACD--I really like this one and the sound is both clear and atmospheric). At least two more are coming: Zinman and Tilson Thomas. There is or was a DVD with Rattle, but it was actually a DVD video with just music tracks, not a DVD-A. There was also a DVD-A with Chailly.

On redbook, the performances that people seem to like the most are Solti, Tennstedt, Boulez, Rattle. These are all very different from each other. The Solti performance is very dramatic and hyper, and IMO the recordings is multi-miked and congested. I found Boulez boring. My faves are Rattle and Haitink. Least favorite is Abravanel (poor soloists, weak strings) and either of Bernstein's (both have ruinous sound in different ways--the CBS is an echoey mess, the DGG is a live performance and is very congested with no soundstage to speak of). Shaw's has good sound, but it's really boring.

I don't think either of these would be hard to find online; for example, the Haitink is at
http://www.arkivmusic.com/classical/album.jsp?album_id=129002&album_group=4 (back-ordered)

or
http://www.cduniverse.com/productinfo.asp?pid=7105919&style=classical

The Rattle redbook is:
http://www.arkivmusic.com/classical/album.jsp?album_id=100241
or
http://www.cduniverse.com/productinfo.asp?pid=6842966&style=classical

P.S. I don't work for either of these websites, and there are plenty of other places to get these discs.

Pbarach,is the sacd version of Haitink's the same one as on Philips's red book or is it a different recording?I've got the one on red book and really love it,so,if it's the same on sacd,i'll get it.

Haitink has made only one recording of Mahler 8, which was set down in 1971. Phillips released it on LP in 1971 and later on redbook CD. The same performance was released in the last year or so on Pentatone as a hybrid SACD. The Pentatone includes a multichannel (4.0) SACD track, a 2-channel SACD track, and a redbook track. I don't know if the redbook track on Pentatone is a remastering of what Phillips released before, but it's definitely the same performance. Either of the SACD tracks on the hybrid is a major improvement over the redbook track on the same disc, I'll say that...
BTW, here is a pretty complete list of all recordings of Mahler 8 to date: http://gustavmahler.net.free.fr/symph8.html