The mainboard

So, the mainboard!
Depending on your budget, you might want to get a mainboard with integrated graphics
if you're low on cash and buy the graphics card later.
The board will be AM3 of course. Also I suggest you to get an asus board because
I had the best experience unlocking the fourth core on my Amd and thats what others also say..

I suggest to get:
with integrated graphics onboard:
ASUS M4A78LT-M LE VGA/GBL/R/D3 AM3  which is arround 55€ or
ASUS M4A785TD-M EVO which is the mainboard i use, around 60-65€
ASUS M4A785TD-V EVO/USB3 VGA/D3/AM3 for 100€ the catch here is that it features USB 3, which is nice to have for the future..

Well, most mainboards in this price ranges have graphics onboard, but dont worry about it..
Please avoid this:
ASUS M4N68T Pro GBL/R/DDR3 AM3  
The data rate is so low on this, its just not worth the 60€ you would pay for this, also no graphics.

Apart from that, you can really take whatever you like.

Keep an eye on:
The data rate(which should be 4000+)
The Cpu compability(am2, am2+ and am3, you DO want am3)
Does it fit in your computer case if you already have one ?
The type of memory which can be used(you want ddr3 with atleast ddr3-1333, which is completely fine)
And you do want sound onboard, since you're going for a low-budget build.