You could use something like compilr.com, however, it requires a paid account (as of June 2013) to create projects but people can view it anonymously. It's pretty neat. (compilr closed down)
Example:
http://compilr.com/cravecode/test-share/main.cs
UPDATE 1
I'd also checkout coderun.com/ide (no longer available)
UPDATE 2
Check dotnetfiddle.net which has Context menu as well (pointed out by @wulfbane).
UPDATE 3 (2017-03-19)
Keeping answer updated, I now use:
- https://csharppad.com
- http://rextester.com (has a really neat collaboration feature)
- https://dotnetfiddle.net
You may also want to check Ideone (has no context menu)
