KaKeeware Browser is the smallest browser in the world.
The goal was to prove that impossible is possible ;). The size of the executable is 2868 bytes and its size can be even smaller* - the file is packed with UPX and then rebuilt with LordPE. The proggie is just a simple dialog-box with the Internet Explorer OLE Control (IWebControl2) embedded on it.
There are two versions of KB available (kb_ie.exe and kb_mo.exe) - the only difference is that one is using Internet Explorer ActiveX and the second one is using Mozilla ActiveX (it has to be installed to make kb_mo.exe work).
Sources (kb_ie_mo_src.zip) are freely available (please don't mind my spaghetti code ;). If you happen to use my code, it would be nice if you credit KaKeeware.
* upack can reduce the size to 2352 bytes
Other approaches
As it seems, there are other ways to reduce the size of the application that is supposed to show HTML content.
See KaKeeware HTMLDialog and KaKeeware LaunchIE examples.