yes, there are better backpacks for rain resistance.

my current fave is a very lightweight Outdoor Research model. rolltop closure like a drybag, sealed seams, completely waterproof fabric. you could also sport an Ortlieb messenger bag (all ortlieb messenger bags are backpack style) Arxteryx also makes some rolltop daypacks.

you can pick up a daypack sized rain cover for your existing backpack at any good outdoor supply house like REI, Campmor, etc. Jansport makes them, Dana Design makes them, etc.