How do I get ubuntu to recognize my monitor's proper resolution again?

From the command line, type sudo nano /etc/X11/xorg.conf and look for the screen section (starting with the line that reads Section "Screen"). You'll want to add your resolution for every "Display" subsection below... the format should be self-explanatory.

Just in case... Control-O saves in nano, and Control-X exits. Feel free to use another editor if you don't like nano.

Arr. Tried edciting xorg.conf and restarted X, to no avail. In trying to go through the auto-configure routine again, it displays the list of resolutions, and there's no button I can actually press to include a new one (or even remove an already included one!). What do I have to do to change the selection?

If you go throught the dpkg-reconfigure routine you will eventually see a list of screen resolutions. Use the up and down arrow keys or the tab key to move the cursor, and use the space bar to place an X on your selection. Then move to the OK button and hit Enter to go to the next screen.

I'm actually in the same boat, in that the list of available resolutions in my dialog box is not the same list in my conf file, even after editing, reconfiguring, and restarting.

I'm not 100% sure on this, but you might try renaming your current xorg.conf file to something else (xorg.conf.old or xorg.conf.backup both work) and then running "sudo dpkg-reconfigure xserver-xorg" .. this makes sure that dpkg-reconfigure runs without 'seeing' your existing xorg settings (since it will look for xorg.conf and not find it, because you renamed it). It should be like running it totally fresh. If that doesn't work, then you'll just want to edit xorg.conf by hand, as a superuser, and insert your desired resolution into the list of possibilities. It's really not that hard to do, although the first time you edit a config file it can be intimidating. You'll see a section of the file where on one line it'll give a bit depth (e.g., "16" or "24") and then on the next line, various resolutions, also in quotes ("1280x960" "1024x768"). Add your resolution in on that line, save, and restart.

This is a driver issue. What graphics card are you using?

Oh wait, nevermind. Ignore me.

This is a driver issue. What graphics card are you using? Oh wait, nevermind. Ignore me. No, you're right (unless I've missed something in one of the replies here). The quickest and most pain-free solution here is to install the proprietary drivers for the graphics card, assuming that you're running an nVidia or ATI card. Ubutnu makes this easy nowadays. I think you've just got to select it using the notification area/system tray icon that handles proprietary drivers, at least on 7.04. Once you've done that, add the entry to your x.org config file, as people have described (or just alter the one that's already there). You probably won't be able to get 1280x1024 using the open source drivers without a lot of fiddling around, which might be beyond your skill level (right now!). The incorrect resolution is a notorious problem. Once you have the resolution you want, and as your knowledge of Ubuntu/Linux improves, you can work on switching back to the open source drivers.