Scattered (but unconfirmed) whispers of a high-end server coming from Apple have been mentioned in the past -- but with no real confirmation.
MacBidouille adds to these with a rumor that Apple is working on a high-end server (codename: Dark Star) with support of up to 64 G5 Processors. According to the site, the new machines would be priced between $12,000 and $500,000 [article originally said $50,000, now $500,000] and targetted at clients such as Industrial Light & Magic, Genentech, Pixar, and NASA.
No further information or corroboration of this rumor is available.
Update: Some new reports suggest that this rumor is not true.