first a good psu if you don't have one already. recommendations:
corsair cx 500 v2
antec neo eco 520
seasonic s12ii 520
then, gfx card.
for low budget ($100-140~),
radeon hd 7750 1 gb gddr5
radeon hd 6770 1 gb gddr5
radeon hd 7770 and 6850.
mid range budget ($170~),
radeon hd 6870 1 gb
higher end budget ($250-300~)
radeon hd 7850 2gb, radeon hd 7870 2gb,
even higher - nvidia geforce gtx 670 2gb.
higher end cards can play demanding games like bf3, metro 2033 on higher settings than lower end cards. for your 19" display which i assume has max 1440x900 resolution, a radeon 6870 should give plenty of performance for price while a gtx 670 should be able to run two 19" on max settings i.e. overkill and probably way over budget.
asus, msi, gigabyte make good gfx cards based on both amd and nvidia gpus. asus direct cu ii cards, msi's twin frozr ii, iii, hawk, lightning, cyclone cards, gigabyte windforce cards have good gpu coolers and good performance.
sapphire, his and xfx build cards based on amd gpus. sapphire's dual x, vapor x, toxic cards, his' iceq, iceqx cards, xfx's double d cards have good coolers and performance.
evga builds gfx cards on nvidia gpus. their cards have good performance.
other factors to look out for are, aftersales services like warranty, rma, bundled extras etc.