Let's start with something I'm going to try to make time for during the coming weeks: try out the latest OpenSolaris release. Reviews have been very positive, and my last Solaris experience being with Solaris 9 on my UltraSPARC machine, this seems like a good time to get re-acquainted with this heavyweight operating system. OpenSolaris is surely an interesting addition to the Free software landscape, and it deserves a chance.
Another Free software related thing which might be good to try is the latest KDE 4.2 beta. As some of you might remember, I personally wasn't particularly impressed with KDE 4.0, and 4.1 didn't exactly blow my socks off either - despite the massive improvements made between 4.0 and 4.1. KDE 4.2 is on its way, and a few days ago the second beta was released, and if there's an empty timeslot somewhere, I'll be sure to give KDE 4.2 a go, to see if it has reached a state where I might consider using it as one of my desktops. If you've personally been bitten by KDE 4.0 too, KDE 4.2 presents a good opportunity to see if they made any progress.
Moving on to non-Free software, something high on my list has been to move "full-time" to using Windows 7, build 6956; this build is very close to the actual beta, and has all the fancy stuff enabled (contrary to the build handed out at PDC, which was build 6801). I already have it installed alongside Windows Vista, and I have been using it as my primary desktop for a few days already. There certainly are some niggles here and there, and there are rough edges, but you really need a magnifying glass in order to find them. There are a few bigger problems, too; for instance, Windows 7 doesn't come with a mail client, referring you to the rather dreadful Live Mail application instead.
All in all, this is absolutely nothing like the early Vista releases, which were practically unusable until they hit RC stage - and even after that it wasn't exactly all pink ponies and rainbows. In any case, using the current Windows 7 builds fills me with confidence that 7 might actually be a good product, a feeling I haven't had in a long time when it comes to Windows.
I'm sure you can come up with some more suggestions, so fire away.