Is there a way to hookup two monitors to an Intel Mac Mini?

Only the 2009 ones support spanning. If you bought a new one today you would be able to use dual monitors.

There was a gadget you could get in the days of the PowerPC minis that would let you plug two monitors into it—it faked out the mini somehow. I’m not sure how well they worked, or if you can still get one now.

If it’s not a 2009 model, you could use a USB video card with a DisplayLink chip and the latest drivers – something like this model works fine according to this guy.

Matrox make a non-USB adapter that is quite often cited for this use and is compatible with PC and Mac – it spoofs the resolution of both monitors into one big monitor the Mac detects, if I’m not mistaken.