We picked up this book, Canon EOS 50D Digital Field Guide by Charlotte K. Lowrie to learn how to maximize the benefits of this camera. I was already impressed after reading a few chapters as the information was clearly explained and the content was applicable to both amatuer and professional photographers. There was a good number of supporting photo examples, which is a plus for me as I am a visual learning type of person. I attempted to read through parts of Fundamentals of Photography: The Essential Handbook for Both Digital and Film Cameras by Tom Ang and I would recommend the Digital Field Guide over that any day. The issue with the Tom's book was that it was written in an extremely convoluted manner and required a lot of re-reading.
Accessories
Photography experts recommend buying backup batteries. The battery that came with the Canon EOS 50D, BP-511A, lasts for approximately 800 shots. For someone out in the field, back-up batteries is a must since missing a photographic moment due to battery failure or drained battery is a huge loss. The question I was faced with was whether or not to buy a Canon battery or a 3rd party battery.
Advantages to buying Canon:
If something in the camera fails due to malfunction in the battery, Canon will fix it provided that the warranty is still valid.
Canon is a trusted name in quality so there is less risk of buying a bad battery.
Disadvantages to buying Canon:
EXPENSIVE!!! Canon is atleast 3 times more expensive than 3rd party batteries.
Thats about it.
Although the advantages outweighs the disadvantages, I read on several forums that Sterlingtek manufactures quality and reliable batteries that exceed the power capacity of Canon's (by 30%!). User reviews were mainly positive and the occasional negative comment was because they received a dud.