I've found a great PHP script that can essentially turn a web server into a virtual browser. The script is small and lightweight compared to existing solutions (just 62KB) and it isn't dependent on anything else. I needed it for sending/receiving data through POST (because GET is easy), and more importantly, doing it over SSL. I still need to figure out how to upload files through this, but I don't think it should be too big of an issue. I'm sure it's just a matter of encoding.
The script was found at PHP Classes, a resource I regularly tap into. You'll discover that PHP Classes requires registration, but it's free and you can disable any email notifications. Also, don't be turned off by the website's aesthetics, they were apparently going for "functional". Hey, it worked for Craigslist.