This is a list of a few resources a friendly hacker at MSU shared with me during my junior year. They're catered toward experienced web developers looking to learn a little bit more about web security (ala me). I thought a friend on Twitter could use them, so I'm sharing them for anyone else who may be in that position :)
Begin quote from friend's DMs
This is what helped me get me feet wet with web security problems: http://overthewire.org/wargames/natas/