There is a simple http server API that allow you do some simple stuff quickly, without any addition dependency/installation required.
Are there any similar API/libra
A quick Google gave me many examples of this, such as Creating your own web server using C#.
Note, that is a very old article, there are probably more concise ways to do this now.
Edit: another nice example here.
HttpListener hooks into HTTP.SYS even without IIS, I believe.
You'll need to add priveleges to the service account, though - netsh
on vista, httpcfg
on xp ("how" covered here).
In addition to the previously mentioned webserver project on codeplex, which I've used in a production application, another simple HTTP server API option is Kayak. Kayak appears to be in an early development stage. It hasn't reached 1.0 yet.
UPDATE: I noticed that my original link to Kayak broke recently. The main website for Kayak has moved to http://kayakhttp.com/ but the code is hosted on Google code: http://code.google.com/p/kayak/.
UPDATE 2: Apparently, the Kayak source code has moved yet again, this time to GitHub: https://github.com/kayak/kayak/.
UPDATE 3: the webserver is "being migrated" to a networking library, also at GitHub: https://github.com/jgauffin/griffin.networking