I ran Cydia and installed Installer earlier today. The default Installer sources list a gazillion cool applications, including a few that I couldn't live without: Guitar Tuner and iPhone Video Recorder. I'll also install Funambol and see if I can sync my contacts list between GooSync and iPhone.
Another important application is SwirlyMMS, an MMS client. (Why doesn't iPhone include a native MMS client? The lack of a video recorder and an MMS client almost stopped me from buying the iPhone). To configure SwirlyMMS, I used these settings:
MMSC and Proxy Server Settings
MMS-specific APN Settings
I successfully sent an image from the iPhone to my email address, so I think it works.
I replied, sending email from my PC to my phone number and attaching a different image file. The iPhone received it as an MMS. To view the MMS, I installed MobileFinder and MobilePreview.
It's a little crufty, but it works.