I currently am recommending the Dell Optiplex 790 minitower. (This will work for the desktop configuration as well.) It took me a lot of time and multiple returns to figure out the best way to do dual monitor, triple monitor and quadruple monitor setups (two monitors, three monitors and four monitors). Here is what I found works the best:
Dual monitors: The simplest and cleanest way to do it is to buy a DisplayPort to DVI (male to male) 6 foot or 10 foot cable. The 790 has the capability of using the DisplayPort jack in the back as a second monitor without buying another video card. Here is an example of the cable. Note: this will only work for you if one of your two monitors has a DVI (white) jack. I have also used a DisplayPort to VGA adapter successfully over the last month (this is the exact adapter). You are able to choose either a cloned view or independent screens using either Windows’s Display settings or Intel Graphics settings (click here for Intel’s instructions).
Triple/quad monitors: I found that I couldn’t use my trusty Radeon 7000 PCI cards in Windows 7 machines, so I chose to go with the ASUS Radeon HD 5450 PCI-Express (here is the Amazon link). I chose this video card because it is reasonably priced (with no need for gaming) and that there is no fan to reduce the chance of failures. In the 790, you can actually buy two of these PCI Express video cards and put them both in! (See this PDF for motherboard card slot info.) I’ve done it and it truly works with three monitors and I’m sure it would for four.
Please comment with your own experiments and successes on the 790 or similar models.