What GPU-APU configuration should I buy for mining Bitcoins?
It's essentially too late to be worthwhile GPU mining because FPGA's are much more energy efficient, and cheaper to buy per unit of output. This has meant the difficulty has risen high enough that you won't cover the cost of your electricity (or your hardware) with GPUs. ASICs are likely to be shipped soon, which will largely make FPGA's obsolete. You can pre order ASICs from multiple manufacturers; Butterfly Labs is one.