I use these to get more PCI-E power plugs.
http://www.newegg.com/Product/Product.aspx?Item=N82E16812198018If I -have- to use a molex to get more PCI-E power plugs, I use the ones included with Sapphire cards. They're single molex, not double, and there are no missing wires in the PCI-E pwoer plug, unlike the ones I see in this thread. Their wires are pretty thick, so they don't get hot.
I avoid using them because I noticed some instability when I used one of those Sapphire 1x 4pin molex to 6pin on my then 5830.
When the cables get hot, that usually means that the psu is overheating and/or under severe load.