And Avantext:
Aircraft maintenance manuals and TechPubs Libraries from Avantext
I'm not a complete expert in this area, but from my little knowledge (hey, it's an Internet forum after all, I'm allowed to ramble on about topics I know nothing about), ATP and Avantext seem to cover most things from a GA perspective.
The MO I'm involved with use Avantext for Lycoming and Continental engine information. We had Cesview for two specific libraries of common aircraft we work on. However, we've just upgraded our ATP subscription from the BE4 package to BE4A. This new package now includes all the Cessna library digitally, rather than only on Microfiche. Therefore, I can't really see us using Cesview too much in the future. Although, Cesview now seem to do online library updates, without having to wait for new DVDs to be delivered.
I'm sure someone will be along shortly with a more informed opinion!