1. New Desktop - First off is the new desktop, featuring a new menu bar, a snazzed up dock and "Stacks" to help you keep your desktop clean. For instance, there's a default Stack that collects all your downloads in one place on the dock.
2. New Finder - More on the aesthetics side, Apple is going with a unified look for apps, which nixes the brushed metal style and instead mimics the current iTunes theme -- surprise, surprise. In fact, the new Finder looks and performs almost exactly like iTunes, all the way down to integrated Cover Flow for shuffling through your files. You can also save smart searches in the "playlists" side of the interface. On the back end of things, Leopard includes "Back to my Mac," which keeps track of your home Mac's IP address through various (and secure!) magicks, letting you browse your files remotely as if they were on a local network. Spotlight search also works over networks now, as expected.
3. Quick Look - Another new Finder integrated function, Quick Look lets you open up previews of most common document types without opening the respective app, and unsupported doc types can be added through extensions.
Keep reading for the rest!
4. 64-bit top to bottom - Apple is supporting 64-bit in Leopard from apps to drivers (and presumably beyond). Leopard should run on most Tiger-supporting Macs, just in case you were wondering if the lack of a 64-bit processor in your current Mac (i.e. Core Duo or Core Solo) would lock you out of using the new OS. So don't chuck that first-gen MacBook just yet.
5. Core Animation - Same song as last year, but enough crowd pleasing effects to make it worth a second gander.
6. Boot Camp - Sadly, there aren't any surprise Parallels-killing functions here, but the lack of need to burn a drivers CD should take this one out of the hax0rs' court and see more users taking advantage of it. Also, it will supposedly feature faster switching between from OS X by using the hibernate / safe-sleep feature to keep "open" running apps when jumping over to Windows.
7. Spaces - Once again, not much new here, but it does turn out that you can have more than four Spaces, the number of 'em is user configurable.
8. Dashboard - Yeah, 10 new features? Not so much. Web Clip still sounds fun.
9. iChat - Now features tabbed chats and uses AAC for audio, along with those other fancy features like Photo Booth effects mentioned last year. You can also show off any Quick Look-supported document over a chat, movies included.
10. Time Machine - Backup for noobs, and previews in Quick Look
So no multi-touch interfacing or anything fancy like that, but still a crowd-pleasing offering. $129 and she's yours, come October.