A few of the changes I would like to see on Leopard (or by the time it comes out):
- iChat - multi-service simultaneous logins, along with the MSN and Yahoo support
- Dock - multiple docks, as well as, dividers, and have applications minimize to their dock positions when they generally only use one window.
- Finder - more steamlined, and speedier with better live updating of file and directory information; added path integration and an optional address bar; better integration of Spotlight; and adopting the Tiger Mail look for Finder
- Safari - fixes to the engine, so all pages look as they should (its only specific pages that don't look right, and its very few of them scattered about); even more streamlined and faster; customizable toolbar; better managing/updating of plugins
- QuickTime - more codecs or at least updates to older codecs
- iTunes - allow for syncing of entire libraries between specific accounts on different computers on a home network
- Virtual PC - better integration with OS X (this should not be too much trouble since they are moving to x86 architecture and assuming that Microsoft and Apple can play nicely

)
- Address Book - change the look to that of Tiger Mail, so it looks better together along side Mail
- Sherlock - do something with it, anything to make it more useful again. I still use it for movie times and movie info, but thats mostly it. It hasn't seen a big (much needed) update for a while, and it seems like Dashboard is taking over its territory, because for just about everything on Sherlock, there exists a Dashboard widget that can take its place, and in some cases, be better than going through Sherlock.
- Backup - make it built-in with OS X
- iWork - come preinstalled with OS X on all Macs (with better word processing on Pages, along with a heck of alot better .doc support and importing/exporting to .doc)