Looks like FiLMiC is still buggy (too few reviews to get a good idea). I did find Camera Plus Pro claims to shoot in 640x480 (with live video filters), but it doesn't look like you can select beyond that.
1080p is just too much for me. I don't have the storage capacity for that kind of resolution. I'd love to hear if anyone else has luck with FiLMiC Pro with an iPhone 4S.
I have sent an email to the developers of ProCamera and Camera Genius to inquire about whether their apps allow one to choose resolution for video recording. Will let folks know if I hear anything.
Update: FiLMiC really looks to be the perfect app for me (4 resolution settings). They are very active on their Facebook page and it looks like they are working on an update as of Friday, Nov 4, 2011 for a bug that may not even affect all users.
Update 2: Heard back from both developers: Camera Genius says they don't offer the ability to select resolutions but are considering it for future releases. ProCamera says: "ProCamera offers exactly the feature you were asking for. While in video mode, you can choose from different resolutions via the menu on the right."
So now to decide between ProCamera and FiLMiC Pro...