Cabal and Layered Tools
The cabal is a standard interface for building and installing Haskell tools. I'm very pleased that there are already some tools layered on top of it, like dh_haskell, for building Debian packages based on Cabal Haskell packages. cabal2rpm is a similar tool for rpms, Hackage (implemented on Linux with a Haskell SQL interface) is a Haskell Package database. Hackage will eventually implement an apt-get type interface for installing packages and their dependencies. Haskell support for visual studio is also layered on the Cabal.
Maybe someone (maybe me) will implement some Eclipse plugin for Haskell based on Cabal. Though I can never get Eclipse to work.
I'm really happy that a lot of people are hacking on Cabal and making really great feature requests and bug reports.