It also depends what you mean by second to last model.
There are two main classes of PowerMac G5 - the first models had PCI and PCIX slots and and AGP graphics slot.
The later models introduced Oct 2005 had 2 x 4-lane PCI-E, 1 x 8 lane PCI-E slot and one PCI-E x16 video slot.
The first model you have a big challenge to find multiple PCI video cards that are Mac compatible.
The second model you have a slightly easier but still daunting challenge to find PCI-E cards that are Mac compatible and that will fit the slots.
The cards have to be originally made for Mac, or they have to have be Windows cards which have had a Mac compatible firmware blown into their EEPROM (an operation done on a PC machine, with a moderate degree of risk of bricking the card)
Most Apple supplied video cards are capable of running 2 monitors (not 30" monitors though) with the appropriate cable adaptors
CanadaRAM supplies RAM memory, drives and upgrades to Mac owners all over Canada http://www.canadaram.com