Docs to go is a free option to install with OS 4.5 it is limited unless you pay for the upgrade. It let's you update right from the app. Will also give you a trial of the plus features.
Posted from my CrackBerry at wapforums.crackberry.com
Docs 2 Go from DataViz is the way to go, if they support your particular phone. Their premium version gives you PDF To Go, whereby you can drag and drop pdf files from you PC to your BB ($50 +) RIM chose DataViz on their first offering of Storm, so DataViz must have something to offer.