Guru3D has a great new guide up to help with ideas in building your new PC. They have divided them into three catagories:
The gaming target for the low-end PC:
Target Resolution: 1024×768 with 2/4x AA and 4/8x AF, 1280×1024 with 0/2x AA and 4/8x AF
The gaming target for the mid-end PC:
Target Resolution: 1280×1024 with 2/4x AA and 8/16x AF; 1600×1200 with 0x AA and 8x AF
The gaming target for the high-end PC:
Target Resolution: 1600×1200 with 4x AA and 16x AF or better
Head over to Guru3D for the complete guide.