I've found some great things by googling. Story rec lists, of course. But also meta questions i.e., questions on character motivation and historical background as it would apply to Steve Rogers. (I found a great series of articles with specific information on NYC in the 1930s, including background on the neighborhood Steve grew up in, etc.)
I just type my question into Google and most of the time I find all kinds of interesting links to fannish meta on tumblr, LJ, etc. I started doing this when I noticed fic authors would often use the same "original characters" for villains, allies, etc. Then it occurred to me these were probably canon Marvel comic book characters, and most of the times they were. (This was also how I found out that Hawkeye's wife in Ultron was canon from one comic book series.)