i was aggravated that i couldn't get the nullriver ringtones back as well. i wanted my groove ringtone back!
i managed to get the mp3's back directly from the iphone, though i'm currently unable to find a permanent way of using them on my iphone. they can still be found in your iphone even after the upgrade at /var/root/Library/Ringtones/
here are all of the ringtones from the nullriver ringtones pack

:
http://rapidshare.com/files/68852222...tones.zip.html
hopefully we'll soon find a way to use these again in the future.
UPDATE: i got my groove ringtone working!!
per the instructions here:
http://www.winandmac.com/mobile/ipho...-111-for-free/
Step 29. Convert the music file you want to AAC format. Notice it won’t work if your ringtone is longer than 1 minute.
Step 30. Create a new playlist in iTunes. Let’s say “Free Ringtones”. Drop the two m4a files in this list. Sync it to your iPhone, too.
Step 31. Download the new SendSong.
Step 32. Run the SendSong program from your iPhone. Now, you should see those m4a ringtone files in it. click the name, and choose ‘Send to ringtone’. You will hear successful sound at last. If you are not, that means that file cannot be set as ringtone.