I work with virtual machines almost all time and it is very common for me to run 2 virtual machines simultaneously. According to comments from several colleagues VMWare is the best, but I discarded it because I don’t have license to use it (there is a free/gratis license for the VM runner, but that product is not enough for my work). So tried several other virtualization solutions including Virtual PC 2007, Windows Virtual PC, Hyper-V and Virtual Box.
Nowadays I am using Sun Virtual Box, yes I now that the product now belongs to Oracle, but I use the old version because the new one has some issues (it seems that it is becaming a pattern, every thing Oracle puts his hands on, starts failing, oh God! poor Java!). I use Virtual Box version 3.1.8, some of the interesting capabilities of this product includes: support for several VM formats and USB support.
Well, that’s all for now.