I am thinking about cross-platform with nice programming language bindings (Java, Ruby and Python). What would be the \"flattest\" learning curve but yet enough powers to p
If Java is your preferred language, consider Groovy. It is a really nice dynamic language that sits on top of Java, and has some really nice features (SwingBuilder) with respect to writing GUIs. If it wasn't for the fact I'm highly productive in Tcl/tk, I think Groovy would be my personal second choice even though I'm not a big fan of Java or Swing per se. Groovy looks to take a lot of the tedium out of both of those.
For more information see GUI Programming with Groovy.