Molex connectors will allow you to add more fans by plugging them right into you power supply. If you already have fans, and these fans are 3/4-pin, then you can get a 3-pin to molex, or 4-pin to molex adapter for each fan. If you don't have fans already, just look for some that have molex connectors.
Note that these fans speeds will be constant, and if you want variable speeds for these news fans you'll need to purchase a fan controller of some sort.
Well if you buy normal fans with the '4 pin molex' connector... you just chain them all together and connect it to a 4pin connection from the power supply... and they all just run when the comptuer is turned on
If you go the more expensive route, you get fans with the connection you're talking about (that slip right into the motherboard) - but you connect them to a front mounted fan controller