F#: CTP, Solver Foundation, F# for Scientists
C# CTP is available here, Solver Foundation here:
“Solver Foundation is a framework of solvers and modeling services enabling planning, risk modeling, and scheduling for .NET developers. It is integrated with the full power of the NETfx 3.5+ platform including LINQ for declarative binding to enterprise databases. Solver Foundation is delivered in a single, compact, CLS-compliant library. This managed code library may be used from any modern CLS-compatible language (F#, C#, C++, IronPython, etc.). It aides quantitative analysts, modelers, and programmers in making feasible, near-optimal, and optimal decisions in business critical settings via applications or Office-based solutions. Solver Foundation ships with several production grade solvers and provides easy third party solver integration.
A Solver Foundation program is a declarative model embedded in familiar NETfx design patterns and development environments (Visual Studio 2008). The model is solved by application of numerical and symbolic solvers, meta-heuristics, constraint processing algorithms, and advanced local search techniques. Included in this release are model pre-solve and validity checking. These Solver Foundation services may be leveraged by any of the solvers and provide a rich set of tools to aide to modeling, solving, and post-optimality analysis. Solver Foundation provides these scalable and performance-driven solvers and services while supporting integration with industry standard modeling and serialization formats. This permits users to leverage existing modeling investments directly within Solver Foundation-based solutions.”
You might also want to buy F# for Scientists

C# CTP is available here, Solver Foundation here:
F#*
Sounds really cool. Finally something usable from a major software company
If you’re not buying into vaporware, this has been around for a while, embedded in Java and supported in Eclipse: http://www.ateji.com/optimj.
It’s proven, supports the best solver engines and comes with extensive documentation and samples library.