The highest resolution in the launcher's drop-down box is 1280x1024, and my monitor's native resolution is 1920x1200. Also I'm using the 12/1/09 nightly build.
I tried re-downloading the launcher, nothing, and I just updated the build I was using today. The download took quite a while and I'm about to go to sleep, so I'm not going to try re-downloading that right now.
I realize that your problem has been solved, but I am curious about your configuration, because in looking at the code, the launcher should detect all resolutions.
Do you have multiple monitors connected?
If so, are they the same size?
If not, what is the native resolution of the other(s)?
What is/are your desktop resolution(s)?