I'll be "that guy" and say start with JavaScript/HTML5 plus a NoSQL database system like CouchDB.
The reason is, this combination (like it or not) has a very good chance of completely taking over a wide spectrum of applications within a couple years (web, mobile, tablet, server, and desktop). Java and especially Ruby might be trendy now, but I am starting to believe the days of mega-sized application layers are numbered. JavaScript + HTML5 + touchscreen stuff on the iPad is already hot, and not to mention really fun to play with and learn.
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I'll be "that guy" and say start with JavaScript/HTML5 plus a NoSQL database system like CouchDB.
The reason is, this combination (like it or not) has a very good chance of completely taking over a wide spectrum of applications within a couple years (web, mobile, tablet, server, and desktop). Java and especially Ruby might be trendy now, but I am starting to believe the days of mega-sized application layers are numbered. JavaScript + HTML5 + touchscreen stuff on the iPad is already hot, and not to mention really fun to play with and learn.