One more vote for the 15, 43, 77 setup. This is my travel kit also, but I pack those three into the little black DA Limited three-lens case, which means I can put one more on the body. That is usually going to be either the 31 or, when I re-buy it, the DFA100WR, depending on the situation.
If you are not as attached to the FA Ltds as I am, (and you probably aren't
), then I think a good, simple setup is the 15 plus the Tamron 28-75. That Tamron has quite a bit better IQ than any of the superzooms. Only downside to this is that you don't have anything faster than f/2.8. It is tempting to just add one fast prime, but if you do that, then I'm back to my original recommendation of the 15,43,77.
As far as the tripod goes, I am someone who uses a tripod more than most, but even I would not drag one all over Europe. I would suggest alternatives such as the string/screw/washer method or the new stretchy cord-things that attach to your belt or waist-line of your pants. These are also much faster than setting up a tripod and thus you may get more of the now-or-never type shots.
Finally, the bag. I personally try to stay away from any obvious camera bags or packs. The cities you are going to are not notorious for their crime (though certain public transportation in Rome can be dicey), but there are pick-pockets and "opportunity" thieves everywhere. I would look for something that is not black, is as small as possible, and as comfortable as possible to carry, though room for a few personal items is a good idea.
Don't forget that photos are secondary to making sure that you enjoy what should be a fantastic trip. Have fun!