euro trips!

I have a few mini "euro trips" under my belt and I'm cheap as fack, so I'd consider myself a semi-professional at booking cheaply and reasonably.
  1. My first trip to Europe was in the spring of 2008 (my senior year of college) when I went to London. That's when I discovered the "day pass" for the tube. [1 week]
  2. My second trip to Europe was in the beginning of 2009 (to celebrate graduating college) when I went to London, Paris, Rome, and Dublin. That's when I discovered the goods and bads of hostels and the best diet ever: not being able to afford food. [4 weeks]
  3. My third trip to Europe was in the summer of 2009 (to celebrate my sister's high school graduation) when we went to London, Glasgow, Paris, and Barcelona. That's when I figured out how to survive after my wallet got stolen. [1.5 weeks]
  4. My fourth trip to Europe was in January 2010 when my family went to Madrid, Spain together. That's when I discovered that it's not worth trying to pack my things nicely and neatly if airport security is going to rifle through the entire contents of my bag. (They did this to everyone). [4 days]
It's sort of a personal goal of mine to try and visit as many European capitals before I turn 26 (which is in 2 years and 2 months). High up on my list are Copenhagen, Prague, Lisbon, and Berlin. I keep visiting some places over and over because I love them so much (i.e. London and Paris).

I thought it would be smart and helpful to start documenting what goes into my trip planning so that I could both share and gather useful tips from fellow travelers.