Parallels 5 for Mac has been released, with Snow Leopard compatibility, Windows 7 support, full support for Aero, including Flip 3D in Windows Vista and 7 & OpenGL 2.1 and a host of other new or improved features. You aren't limited to Windows either; Parallels also adds support for OpenGL 2.1 support for Linux guest operating systems. (Although we're a Mac site, I'm glad to see other OSes getting some development attention too.)
It is a free upgrade for those who purchased version 4 on October 1st, 2009 or later. Others will have to pay $49.99USD to upgrade, or $79.99 for a new license.
Parallels is also offering crossgrade licensing to VMware Fusion 2 users. If you have a license key for Fusion 2, you can get Paralells 5 for the same $49.99 upgrade fee as existing Parallels customers.
If you're new to Parallels, check out their introductory video for an overview of how it works.
If you need Windows to go with your Intel Mac, there are a lot of options: Parallels, VMware Fusion (which also recently released a new version), Boot Camp (although Apple isn't yet supporting Windows 7 in Boot Camp), CrossOver, and if you're willing to do a little more "nerd work" to set it up, you can even set up Windows virtualization for free with Sun's VirtualBox tool (well, "free" plus the cost of Windows).
Parallels and VMware Fusion seem destined to be the dueling "favorite flavors" of Windows virtualization on the Mac like Coke vs. Pepsi or vanilla vs. chocolate. Which is the right one for you? Download a demo and take a look. I own both Parallels and VMware Fusion, and look forward to putting them both through their paces with Windows 7.
Thanks to everyone who sent this in.