Go: I actually disagree that it "not ideal for things that change too often". The cost of deploying changes is very low b/c it compiles so quickly. Furthermore, the static typing is extraordinarily lightweight. You have nothing to worry about there.

Lisp: I've only ever used it academically. I'm not fit to comment on it, although my inclination is to say as a founder you should skip it since it's not nearly widely used enough.

Ruby: Works good. (sic) Tons of libraries are a blessing and a curse, though. Also, there's 1000 ways to do everything in ruby...that gets old fast since every library you ever use will chose a different one. All that said, you can't go wrong because of how widely it's used. On the other hand if you're using it solely b/c of rails, then Ruby itself will never really be your main focus.

Python: I have a soft spot for python...I use it to deploy my Go. It's widely used, mature, and I think it's a reasonably good choice. Great for quick file-manipulating tasks as the tools are built in and are easy to remember.

Javascript: Plan on making a web-tool? You're gonna have to learn it. Some of the ugly goes away when you use coffescript. I think you'll need base-level competency at this no matter what other language you choose.

I notice you didn't add C#/Java. C# is actually a really pleasant language to use. The trouble is that you (more or less) have to have a windows back-end to use it.