I've integrated Lua and Ruby into programs in the past.
Lua was pretty easy to get going, but the stack-based API was a pain to work with and pretty error prone, so you'd want to wrap that up so you don't have to deal with it. There's a mod of Lua called LuaPlus which adds some handy features and also wraps the stack-based API nicely for you. Not sure if any of that functionality has made it into the core since then (it was a while ago). In terms of the language, I never really liked it that much - the philosophy of a lightweight language that you can bend to your will is a nice one, but I think they could have built-in some decent OOP support by default.
Ruby was a bit harder to get going. It was never designed to be used as an embedded language, and the source is... interesting (very diplomatic term there). There's also not a lot of info on embedding it - mostly lots of scraps and slightly weird docs kicking around. It basically took a fair bit of digging and experimentation, but it's simple enough once you get used to it. In terms of language, well, I don't think I've ever used a language which is more enjoyable and productive - there's a reason a lot of people are getting into Ruby these days.
Lua is generally quite a bit faster than Ruby, although that's not really an issue if you're using it to automate a program. I wouldn't use Ruby in a game, for example, but then, I wouldn't use Lua either. Don't ask what I would
My overall opinion, having tried both, is that Ruby is worth the extra effort, so long as your program doesn't rely on it being really fast.
Mouser, if you decide to try Ruby out, I can give you some pointers to help speed things up if you want. I could probably help a bit with Lua if you decided to use that, although my Lua knowledge is a bit out of date, and there's lots of Lua info out there anyway.