You can try them at

http://rapid$hare.com/files/93861119/iphonealerts.zip.html

Just SSH them into your /System/Library/Audio/UISounds folder.

Alarm.caf is a Calendar alert
new-mail.caf is for Mail (obvious)
Voicemail.caf is obvious
sms-received6.caf is what I use for SMS. You need to use the "Electronic" setting in Settings > Sounds > New Text Message> Electronic. I didn't like the original Electronic sound so replaced it with this one.

My ojective was to get some sounds I could actually hear. If you like one for a different function, just re-name it. It's a good idea to make backups of the originals.

Actually I didn't "make" them. I've collected these from various places and some of them did take some work to get them to work.

The sms-received sound was from another thread or forum but can't remember where to give credit.