This is going to be unpopular advice, but I would suggest algorithms in C. You already know how to make web applications. Any reason you want to know how to make web applications again? Will Lisp or C web applications make you happier or more productive?

What will help you is probably a better understanding of algorithms/programming and I personally like C for that job. C doesn't hide stuff like higher-level languages do. It makes you think about how the computer processes the information and uses memory. I'm not suggesting that you ever use C for one of your webapps. I'm suggesting that knowing C and good algorithms will make you a better programmer in higher level languages because you will understand more.