Oh! I thread I can reply to! PDAs have been a hobby for me for about 4 years now... I guess that's something to be proud of or embarrassed about... not sure.
I currently have a Sony Clie NX80V that syncs awesomely with my Powerbook. Many people will tell you, including Sony itself, that to get a Sony PDA to sync with a Mac, you need The Missing Sync: a $40 application. This isn't completely true. All basic conduits can be synced using the Palm Desktop software. However, to be able to mount the memory card as a drive, you will need The Missing Sync. I accomplish this with a $20 Lexar JumpDrive Trio, which is like a thumb drive without any built in memory, that accepts MemoryStick, SD, and MMC cards.
I am personally probably going to grab a T5 when it comes out. I'm looking forward to having Bluetooth connectivity between my Powerbook and my Palm. However, it should be noted that the T5 will be a PalmOS6 device. This is significant because with the release of OS6 PalmSource (The company that makes the Palm operating system) is discontinuing official support for OSX. This does not mean that handhelds will not work with OSX, though it does mean that The Missing Sync will be required. The company behind The Missing Sync has been working on a new OS6 version and should have it out when the T5 launches. Personally, I'm optimistic that PalmOne (The Palm hardware company) will work out a license agreement with the makers of The Missing Sync, and the app will be bundled with all PalmOS6 handhelds released by PalmOne. I'm not basing this on any source, this is purely my personal speculation.
So I'd say the handhelds you want to look at are the Zire 72, Sony TH55, Tungsten T3, and the Tungsten T5. I'm throwing the TH55 in there because it's an awesome handheld that can be had pretty cheap now, with a built in camera, 320x480 screen, and awesome form factor. The only downside I see is that it doesn't have Bluetooth.
If you get a Zire72/T3 now, it will support OSX out of the box. If you wait for the T5 you will get much better hardware but may have to pay $40 for software to get it to sync up with the Mac.