AIM Buddy List Back Up?

May not be quite the ticket for what you're after, but Adium works with AIM buddy lists, and can be linked to Address Books. Just a thought

 

Well I don't know about any stand alone apps, but you could always use AOL's official Mac Instant Messanger client.

Use it by logging into whatever AIM account you want to backup, then goto 'File' > 'Export' and it will save all your settings. (you can modify 'Export Options..' to only include backing up of your buddy list if you want so your not saving all the other stuff like connection/privacy/font stuff).

Then if you ever need to restore your buddy list, log in again through AOL IM client and import the backup file you previously saved. So basically you can use the officialy AIM client as your backup app.