Palm LifeDrive Mobile Manager
Palm ($499)
http://www.palm.com/us/products/mobilemanagers/lifedrive/
I bought this directly from Palm with overnight shipping provided by FedEx. I ordered it one evening, it shipped the following day, and I received it the day after that. Very fast turn around time. It arrived in an oversized discreet brown box that contained the LifeDrive box and the bonus CD that comes free with it.
It features a 4 GB hard drive built in, so storage will never be a problem. With my Palm m515 I had 64 MB of space, with the Axim X50 I had 224 MB of space. On both of them I never needed more space, so this 4 GB will not run out, I'm pretty sure. It offers the ability to use it as an external hard drive that I can mount on my desktop. I just transfer my office files, pictures, music, and videos over to it, and the LifeDrive can access/view/edit them when you are away from your computer. This is a very fast and responsive machine.

Taken out of the shipping box. LifeDrive box and the bonus CD.

Contents of the LifeDrive box. Includes software, setup guide, leather sleeve, charging adapter, USB cable, and LifeDrive.

Comparing the LifeDrive with the Dell Axim X50, with their manufacturer included sleeves.

Comparing the thickness. LifeDrive on the left, Axim X50 on the right. The LifeDrive is a little thicker.

This is the included leather sleeve.
I let it charge for the recommended 3 hour initial charge and installed the software. Mac users get a little more love than we normally receive from Palm. The Hotsync Manager includes conduits for syncronizing with Palm Desktop software. Palm also gives us Dataviz Documents To Go for Mac. This allows synchronizing with all of your applications on the LifeDrive, including the Note Pad and and Voice Recorder. iSync (comes with Mac OS X) provides it's own conduits for synchronizing with iCal, To Do, and Address Book.
I set it up to synchronize via Bluetooth but that takes quite a bit longer than with a USB connection, but it does provide the convenience of a wireless synchronization. Pairing the device was rather straight forward.
Included Software
This is the software that I find useful and that synchronizes with something on my Mac.
Updated
It's been a month now of using the LifeDrive every day and here are my thoughts on it. I still love it.
I ended up not sticking with StickyBrain. The included Memo application included with The Missing Sync works perfect. AvantGo conduit with The Missing Sync also works great.
The Missing Sync works well most of the time. There are times every now and then when it starts up but then just quits as if it never started. When that happens, opening it up again makes it work just fine.
I use my ThinkOutside Bluetooth keyboard with it, but it has it's own quirks that I can't seem to pin down a source or consistency. Sometimes it works perfect, other times it has a problem where when I press the shift key to capitalize a letter, two letters get capitalized in a row. I'm sure it has something to do with the fact that the LifeDrive tries to capitalize the first word of a sentence automatically.
The LifeDrive has no problems connecting to wireless networks, or Bluetooth connections.
Contacts and Calendar synchronize flawlessly with my iCal and Address Book.