Connect MacBook Pro to two external monitors
To get a three screen setup (two external screens, and laptop screen) connected without daisy chaining Thunderbolt displays, you need:


One external monitor hooked up to the Mini DisplayPort
One external monitor hooked up from USB to DVI


I am assuming you already have the first item taken care of as it is the easiest.  So, let's focus on the second one:

You need something like the Diamond BVU195 HD USB 2.0 to VGA / DVI / HDMI Adapter.  This will give you your "display adapter" for your second external monitor.

Now, you would set your primary monitor the same way you would in a dual monitor setup.   This article from OS X Daily details it nicely.

When you disconnect, as was mentioned in one of the comments above, your main display will revert back to the laptop screen.

That's it.  You're done.  But if you want to see this working, check out this YouTube Video.

Enjoy!