Portable Programming IDE

Eclipse isn't "minimalist", but it does work installation-less. So as long as your USB key, or whatever, is large enough, you can put Eclipse in there and be ready to go.

alt text http://sts.bkukr.de/l-davoss/blog/Lists/Blog/Attachments/21/SharpdevelopPortable.jpg

Sharp Develop Portable:

Dave blogged all you need to know to get you started!

C# support on the run, and much, much more.

Please have a look at ideone.com - supports 40+ langugages