i would reccomend a last-gen 6870 2gb card. It's very capable, will run 2 and even 3 monitors, and should cost the same as a 7850, but you'll get more stream processors with the last gen 6870.
Correction: -
http://www.hwcompare.com/12078/radeon-hd-6870-vs-radeon-hd-7850/
Even with the higher SPU count on the 6870, it looks like the 7850 has more bandwidth, so that would be my choice. Both are very viable crossfire solutions, the 7770 is not what i would choose for dual monitors.
a 7950 is overkill for 2 monitors, it's a good choice for eyefinity 3 monitor, or 120-144hz single monitor though.