It's hard to generalize, but I would say there are at least 8 non-obscure FP's that either hook into java and .NET libs, or have some level of stdlib and community libs (I've only used 3, and I hear C# is getting some functional aspects, but I'm not following).
- lisps: scheme, CL esp. SBCL, clojure
- F#, scala
- erlang, ocaml, haskell
here's some books, freely available content, including for ocaml and haskell