We found ourselves in the same situation. Perhaps our choice of books will help you to narrow down your purchase...
For Companion Planting, we purchased the following two books:
Our favorite tip:
Borage! This beautiful plant will re-seed itself for the next year as well. Plant near your tomatoes - they love them! Not only that, borage attract bees which will also come across your tomatoes, peppers and other veggies. Other benefits of borage - the flowers look rather lovely in a vase, providing beautiful filler and added color to floral arrangements.
Borage is also an edible salad green, and the flowers are an anti-depressant! Eduardo Machado, a plant specialist from Uruguay recommends eating 7 flowers a day to keep the blues away. They're not bad!
More photos coming soon - please stay tuned!