More .NET languages are popping up everyday.  I've put together one of the most extensive lists of languages and posted it here. 

Its pulled from many sources including: .NET Languages (ASP.NET), Cetus, Language Vendors (MS GotDotNET), .NET Language Group (MS GotDotNET), Visual Studio Partners: Language Vendors (MS), Mono-list, Google, SourceForge.net

• Ada
  • A# - port of Ada to .NET (Dr. Martin C. Carlisle)
• APL
  • Dyalog.Net - Dyalog APL (Dyadic)
• AsmL
  • Abstract State Machine Language (MS Research)
• Visual Basic
  • VB.NET (MS)
  • mbas (Mono/Ximian)
• C#
  • C# (MS)
  • mcs (Mono/Ximian)
  • cscc (DotGNU Portable.NET)
• Caml
  • F# (ML and Caml), Abstract IL, ILX (MS Research)
• C++
  • Managed Extensions for C++ (MS)
  • Managed and Unmanaged C++ (GotDotNet)
• Cobol
  • NetCOBOL - COBOL for .NET (Fujitsu)
  • Net Express (Micro Focus)
• Delphi
  • Borland Delphi and C++Builder Support for .NET (Borland)
  • Delphi.NET - interoperability tools (Marcus Schmidt)
• Eiffel
  • Eiffel for .NET (Interactive Software Engineering)
• Forth
  • Delta Forth .NET (Valer BOCAN)
• Fortran
  • Lahey/Fujitsu Fortran for .NET (Lahey Computer Systems, Inc.)
  • FTN95 - Fortran for Microsoft .NET (Salford Software Ltd.)
• Java
  • Visual J# .NET (MS)
  • IKVM.NET - Java VM for .NET
• JavaScript
• JScript .NET (GotDotNet)
• JANET - JavaScript-compatible language
• LOGO
  • MonoLOGO (Richard Hestilow)
• Lua
  • Lua.NET: Integrating Lua with Rotor (PUC-RIO
• Mercury
  • Mercury on .NET
• Mondrian
  • Mondrian and Haskell for .NET (Nigel Perry)
• Oberon
  • Active Oberon for .net (ETH Zuerich)
• Perl
  • Perl for .NET, PerlNET (ActiveState SRL.)
• Pascal
  • Component Pascal (QUT)
• PHP
  • PHP Sharp
• Python
  • KOBRA
  • Open Source Python for .NET (Mark Hammond)
• Ruby
  • NetRuby
• RPG
  • ASNA Visual RPG for .NET
• Scheme
  • Scheme (Northwestern University)
• Small Talk
  • S# (SmallScript LLC)
• SML (Standard Meta Language)
  • SML.NET (MS Research, University of Cambridge)
• Visual Basic
  • VB.NET (MS)
  • mbas (Mono/Ximian)

I'll try to keep this updated when I run across a new language.  If anyone knows of any others, let me know.[via Brian Ritchie's Blog]