Assuming you have a monitor that supports some high resolution, say 1680 x 1050, and you’re using an nvidia card:

  1. System > Administration > Hardware Drivers
  2. Make sure the latest recommended nvidia proprietary driver is activated (if not, do it and reboot)
  3. System > Preferences > Display (it should ask if you want to use the proprietary config screen – select ‘Yes’)
  4. Select X Server Configuration
  5. Set the resolution to what you want and ‘Apply’, then quit the nvidia-settings screen.
  6. System > Preferences > Display (when it asks this time, select ‘No’)
  7. Click ‘Apply’
  8. Click ‘Keep configuration’ (assuming everything looks OK)
  9. Click Close

When you reboot, everything should be preserved.  I still notice a flicker on the boot-up screen when I think it tries to reset it to something else, but it should stay at the resolution you specified.