MB: ASRock P67 PRO3 (B3) || ASUS P8H61-M mATX
It's enough for your i3-2100. The P67 is you have any plans on upgrading to an unlocked CPU later on
RAM: G.SKILL Sniper 8GB (2 x 4GB) 1600MHz (if you pair it with the p67)
RAM: G.SKILL Sniper 8GB (2 x 4GB) 1333MHz (if you pair it with the h61)
Or any of the other RAM linked earlier in the thread. That said I would switch the CPU to an i5-2400 and get a p67 board, if you can't fit it in the budget stick with the i3-2100.