More bits

I got a shiny new 64 bit computer at work recently. So sometimes when I want to get download software, I have to choose the version with enough bits. Although I have 64 Intel bits, the right version might be AMD64, or any of x64, x86-64 and x86_64. I've never been offered IA-64, but I've read enough to know to avoid that because although that would be 64 bits, they're the wrong kind of bits.