Joining the bandwagon, Karger has just announced its own hybrid journal trial program, entitled "Author's Choice". Under Author's Choice, articles in eight journals can be made OA for a cost of $2,500 US. The journals for which this applies are:
Cytogenetic and Genome Research
Dementia and Geriatric Cognitive Disorders
Medical Principles and Practice
Author's Choice is described as a "trial model". This is likely why only eight of Karger's approximately 85 journals are included in the program.
No mention was made in the announcement of a corresponding reduction in subscription costs (maybe this will come later, after the "trial" period).
The $2,500 US payment is in addition to "any standard charges for supplementary pages, color images etc. which may apply".
More information about Author's Choice can be found on the Karger site at http://content.karger.com/services/choice.asp. Peter Suber has also blogged this at http://www.earlham.edu/~peters/fos/2006_12_31_fosblogarchive.html#116791849595590997
(I blog in his shadow...)