I don't have a desire either, but it sounds like you just removed the widget. Long-press an empty space on the home screen (meaning anywhere there's a blank space, just hold your finger down for a second or two) and an option will pop up to add... shortcuts, apps, and widgets. Click widgets. There should be one for airplane mode.
As jackgibbs said, you can also turn it off in the settings and-- I don't know if this is just for the droid x-- but holding the power button for a few seconds (longer than it takes to just lock the screen, but not long enough to turn the phone off) brings up a menu which includes airplane mode.