Irex DR1000s reads pdfs with aplomb.
I dare say the Knidle DX does a reasonable job too, but I don't have one to confirm.
Most 6" deviced do not do pdfs very well.
Some of teh new 8" devices may well work verywell too for the more casual pdf reading, but for charts, graphs, technical papers you reallly need a 10" display.
"DRM: Distressed Reading Members."