IronPython
IronPython is [http://hugunin.net/index.html JimHugunin's] implementation of Python on the .NET CLR.
The project has a [http://www.codeplex.com/Wiki/View.aspx?ProjectName=IronPython workspace] where you can get news and download the latest version. An older site, http://ironpython.com/ appears to be unmaintained. (He didn't have enough time to do it properly without funding -- so Microsoft hired him. As of January 2006, Microsoft has released a Beta version, and the expectation is betas roughly every three weeks, and a final within 10 betas.)
Early results are promising, showing great performance, even better than CPython 2.3 on the Pystone benchmark, but remember this is an early prototype, not a full implementation.
These results caused a flurry of discussion, which has since died down, pending more information from Jim.
Other Python-Like Languages for .NET/Mono
Some other Python-like languages for .NET and Mono include:
BooLanguage - Syntax is very similar to Python's, yet the language is statically compiled. It implements many features that have been suggested for ["Python3.0"]. See [http://boo.codehaus.org/Gotchas+for+Python+Users Gotchas for Python Users] for specific comparisons between boo and CPython.
[http://www.prothon.org/ Prothon] - now defunct
Accessing .NET from CPython
[http://www.zope.org/Members/Brian/PythonNet/index_html Python for .NET] is the reverse of IronPython, it lets you access .NET assemblies from CPython.
See also: PythonAndParrot, LoGix, IronPython IDE