How can I export a list of currently installed applications to a file? When switching between ROMs, I've found it helpful to have a list of the applications that I had installed before wiping and flashing the new ROM.

Is there a way to export such a list to a file so I don't have to create one manually?
With a Terminal Emulator app (or via adb shell), you can use the following command to get a list of installed applications:

pm list packages


There are some optional switches for this command that will give you more information, such as the location and name of the APK file as well.  Keep in mind that this command lists both 3rd-party app as well as system ones that came pre-installed on your device.

If you are generating the list for the purpose of re-installing the apps on the new ROM, you might want to look into the AppBrain App Market app.  Once you are signed in with your Google account and synced up, it will save the installed apps as a list that you can view and manage online.  After installing a new ROM, you simply download the AppBrain app from the Market first and use it to re-install other apps from the saved list by doing the following:


Launch AppBrain app.
Select the Manage And Sync option.
Sign in with the same Google account as you did before.
Tap the My lists... button and select the list you've created previously.
Tap the Add all apps button.  This will queue up all of the applications you had installed on the previous ROM for installation.
Go back to the previous screen and tap the Execute changes button which will automatically bring you to the Market page for installing the apps.