There is no real "solution" for pleasant reading of PDFs on an ereader if the PDF was designed for a much bigger screen or for printing.
You could try one of the many free PDF cropping utilities which attempt to remove the excess whitespace margins on each page. Here's
a link to Briss available in the MobileRead PDF forum. It's one of the better ones I've tried.
For a
more general discussion of the problems/solutions this may be of interest.