To get a bit more technical about it....
Style
BJCP Style Guidelines - Index to Categories
BJCP (Beer Judge Certification Program) has style guidelines laid out for every style they recognize for competitions. If you want to learn about different styles, how they are designed, how they differ from other styles, this is the most definitive list I've ever seen. This is not a fully comprehensive list though, as many one-off beers don't have any representation except as a "specialty" beer for that style. A White IPA is an example of this, a witbier grist (maybe increased for extra alcohol) and yeast, plus a hop profile that is appropriate for an IPA, would end up being a "Belgian Specialty Ale" (16E. in the style guide). I'm excited to see a new style guide, as brewing has evolved and expanded immensely since 2008.
Yeast
To learn more about yeast, my two favorite yeast manufacturers:
Wyeast Laboratories
White Labs
Wyeast Laboratories Yeast Strain Guide and Yeast Style Guide are great resources for trying to determine the type of yeast that ought to go in a beer (based on their products). Their Pitch Rate Calculator has been an invaluable tool, allowing us to know how much yeast we're adding to each brew to be sure the yeast can properly ferment and complete a diacetyl rest so the beer doesn't taste like buttered popcorn and bandaids (especially important to get a good diacetyl rest for Belgian yeasts).
White Labs is another yeast & inoculant manufacturer. There's nothing much to add beyond what Wyeast Labs has, just different stuff available and how they present the info.
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I hope that this information will help provide a much more thorough and in-depth understanding into all of what goes into making beer, both materials and process.
Next time I post, I'll have some info on Hops and Malt.