Of course if you own any cookbooks you can frequently just check the endpapers for conversion tables.

http://www.recipegoldmine.com/kitchart/kitchart2.html

This is a good site for conversions. I'm based in the UK and have to admit I don't get the cup thing, as conversion isn't straight forward as every item is a little different.

For simplicity, try left hand side of (very ugly website) http://www.thatsmyhome.com/recipes/converter.htm

Here's a tool with basic information plus a calculator, but please remember that flour varies a lot in its weight per volume, due to variations in moisture level (which can be caused by several different factors):

http://www.gourmetsleuth.com/cooking-conversions/gram-conversions.aspx

;o)