No such platform exists for Windows 7.
VMWare: Anything commercial is pay-for.
Sun VirtualBox: License specifically states commercial deployments are not free.
Xen: Doesn't run on Windows.
Hyper-V: Only runs on Server 2008.
Virtual PC: What came before Hyper-V, spotty Windows 7 support, and still not free for commercial use.
Unfortunately, if Commercial = true, then payFor also = true.
The one exception is VirtualBox open-source-edition. There are no pre-compiled binaries that I can find (that doesn't mean they can't be dug up, though), but if you want to take a whack at compiling your own you can do so here, under the VirtualBox Sources section. VirtualBox-OSE is GPLed, unlike the binary distribution which is under a different license and excludes commercial use.