Hi all,
GHC 6.6.1 packages are in Haskell Unsafe (amd64 only, although you can build the source on your arch if you want (please let me know if you try this, regardless of whether it succeeds or fails)):
http://haskell-unsafe.alioth.debian.org/haskell-unsafe.html
Currently the only extralib packaged is mtl (libghc6-mtl-{dev,prof,doc}). More will probably follow soon.
Note that these packages may not be what end up being uploaded to Debian, and they are barely tested at all. Yada yada standard no disclaimer stuff.
Thanks Ian