InfoWorld’s JR Raphael provides an in-depth comparison of Android productivity suites, including DataViz’s Documents to Go, MobiSystems’ OfficeSuite Pro, Quickoffice Connect Mobile Suite, ThinkFree Office Mobile, and the Google Docs mobile Web app. Each tool is vetted for word processing, spreadsheet editing, and presentation management. Raphael also examines additional tools for accomplishing other basic office tasks, such as dealing with PDFs and Photoshop files, piecing together the best overall package for your Android smartphone at work.
I agree with the pick for the top apps in each category. There is also a Djvu reader for android which can come in handy.