If you occasionally want to encode to
H.264, but don't own Quicktime Pro, you can do it if you own
iMovie HD (part of the
iLife suite). Just create a new project, import the file you want to convert to H.264 by dragging it to iMovie (in my case, it was an mjpeg from my digital camera). After importing, go to File: Share. In the QuickTime tab of the window that pops up, choose Advanced settings, and you will have access to all the encoding options you would have in QuickTime Pro.
[
robg adds: I'm pretty sure this is intentional; purchasing iLife (or a new Mac that has it bundled) gives you the ability to export your iMovie projects in any of the QuickTime Pro formats, even if you haven't purchased QuickTime Pro. You won't, of course, get all the other QuickTime Pro features...]