Some time ago, Jeremy Shaw wrote a Parsec clone for lazy ByteStrings.
I've been using it for a while, and have made substantial changes to it
along the way.
It's very fast, using the same manual unpacking trick as the binary
package to keep performance nippy. It also integrates with the latest
flava in parsing combinators, Control.Applicative, providing instances
of the Applicative and Alternative typeclasses.
The API is rather smaller than that of Parsec, but it's more than
adequate for parsing e.g. text-based network protocols.
Download:
http://hackage.haskell.org/packages/archive/bytestringparser/0.2/bytestringp...
Haddocks:
http://darcs.serpentine.com/bytestringparser/dist/doc/html/bytestringparser/...
Darcs repository:
darcs get http://darcs.serpentine.com/bytestringparser