Right now I'm running through SICP with Scheme; I'll look into Common Lisp as well. Arc interests me purely from a webdev standpoint, unless the other Lisps also work well with the web? I've also heard of Clojure but I'm not too interested in compiling to either the JVM or Javascript. Erlang also interested me in the past but I'm not looking into it at the current moment. Maybe one day.
Clojure has good web libraries, and Clojurescript compile-to-js means you can write both the back- and front-end in Clojure. For what it's worth, Amazon's back end used to be C and Common Lisp, and they've recently posted openings for Clojure devs. I mean, even Scheme has web server libraries (and if you want something simple, it's not a bad choice). But if you want a LISP with extensive web frameworks and protocols, Clojure is really it. Arc just doesn't have the popularity—when you hit walls, it's going to be hard to find help.