Take a look at Anxiety, a nifty little to-do tracker for OS X. It uses the new Calendar Store in Leopard so that it keeps your to-dos in sync with iCal and Mail (and therefore also any devices you may sync with iSync). Best of all, it's free!
 

I'm one of those people that needs more than one computer to work. My main workstation is a 15" MacBook Pro that is connected to a 20" Apple Cinema display. To its right is our 20" iMac, which serves as our media server, backup server, and VMware test machine. Due to limited desk space, I didn't want to have multiple keyboards and mice laying around. My first thought was to use a standard KVM switch to switch my keyboard and mouse between my Macs. But that requires a lot of USB cables, and I really didn't want that kind of clutter behind my desk.

Wow.

I've been using Apple's new Leopard operating system for a couple days now and all I can say is that Time Machine alone made it worth the purchase price.

Time Machine is the backup software built into OS X 10.5 that everybody is raving about. Count me in too. Time Machine runs in the background, doing hourly incremental backups of your data to an external hard drive. What makes it so great is that it is painless to setup - just plug in an external drive, and OS X asks you if you want to use it for Time Machine. Click yes and you're done.