If your computer has 2 pci-e slots, then you can get 2 inexpensive discrete video cards.
Each 1 will let you drive 2 monitors. Get cards with 1 dvi and 1 hdmi output, use a dvi-hdmi dongle http://www.newegg.com/Product/Product.aspx?Item=N82E16882021060&cm_re=dvi_to_hdmi_adapter-_-82-021-060-_-Product
If you have only 1 slot , you could get this card , it has 2 display controllers, for 4 outputs. You would need 4 dvi-hdmi dongles http://www.newegg.com/Product/Product.aspx?Item=N82E16814129158&Tpk=4670x2
There are also USB to video adapters that allow added monitors. But they run independent of the gpu driver, and do not know if they support new flash or not ?
Also the new eyefinity cards as mentioned above.