Depending on your budget these are great options:
•CPU: AMD Phenom II X3 720 Black Edition Heka 2.8GHz Socket AM3 95W Triple-Core Processor Model HDZ720WFK3DGI - OEM
•MOBO: ASUS M4A785TD-V EVO AM3 AMD 785G HDMI ATX AMD Motherboard - Retail
or
•CPU: Intel Core i3-530 Clarkdale 2.93GHz LGA 1156 73W Dual-Core Desktop Processor Model BX80616I3530 - Retail
•MOBO: ASUS P7P55D-E LGA 1156 Intel P55 SATA 6Gb/s USB 3.0 ATX Intel Motherboard - Retail
if you have more money think about maybe these:
•CPU: AMD Phenom II X4 955 Black Edition Deneb 3.2GHz Socket AM3 125W Quad-Core Processor Model HDZ955FBGMBOX - Retail
•MOBO: ASUS M4A79T Deluxe AM3 DDR3 AMD 790FX ATX AMD Motherboard - Retail
or
•CPU: Intel Core i5 750 Lynnfield 2.66GHz LGA 1156 95W Quad-Core Processor Model BX80605I5750 - Retail
•MOBO: GIGABYTE GA-P55M-UD4 LGA 1156 Intel P55 Micro ATX Intel Motherboard - Retail.
Obvoiusly this depends on your other parts ram, case, psu and what it will be used for i.e. gaming, internet surfing etc.