python -m SimpleHTTPServer
The webserver runs on port 8000, so to access the pages in your browser, you'd use http://localhost:8000. If you'd rather run the webserver on another port, just include the port number on the python line: python -m SimpleHTTPServer 8080.
Depending on which browser you're using and the files you're browsing, you may be able to open the files in the browser, or via a helper application. Safari, unfortunately, wants to download file types it doesn't know about, which may not be all that useful.
To quit the server, press Control-C in Terminal (does anyone know a more graceful way to do this; Control-C throws a bunch of errors as it quits?).

