AMD Slew X4 640 quad-core with what model of Asus motherboards

The main reason for choosing a motherboard from a CPU is the interface of the CPU and the chipset model of the motherboard. Your CPU is AMD X4 640 quad-core, it is AM3 interface, so certainly have to choose the AM3 interface motherboard, and AM3 interface motherboard according to the use of the chipset model can be divided into high-end, mid-range, low-end, corresponds to the 9, 8, 7 series of chipsets, respectively.

7 series discrete chipsets: entry-level budget configuration

770 general gaming

790X 750 Southbridge, high-end gaming

790FX 750 Southbridge, enthusiast-grade, supporting dual graphics cards crossfire.

8 series chipset: the current mainstream mid-range cost-effective configuration

870

880G equipped with HD4250 display core.

880G is equipped with an HD 4250 graphics card.

890G is equipped with the HD4290 graphics core.

890FX The top end of the 8 series comes with AMD's highest-end hex-core Thuban (SEED II x 6) and quad-core Deneb (SEED II x 4) processors, a southbridge SB850, support for the HT3.0 bus with DDR3-1333 memory specifications, two PCI-E 2.0 x16 lanes, and support for 2X16 or 4X8 CrossFire. Add some I/O bus virtualization technology.

AM3+ interface

970 Regular. Supports standard 1600 memory, overclockable to 2000, and 2×PCI-E X16 graphics slots.

990X 3 graphics

990FX Currently the highest type of enthusiast grade, four graphics slots.

It's up to your usage to choose.