I'm a big fan of tour books for the planning stages of a trip. Nothing gets my travel juices flowing more than a big eyewitness, full-color guide book. Reading novels taking place in my destination--I drool. But lug those thick hardcovers across an ocean--no way!
Instead I often rip out the pages you need or the Lonely Planet feature Pick & Mix, which lets you buy chapters of the books for cheap and print them out yourself.
The best on the ground resources, though, has got to be Mr. Gordonsky's City Spy maps. You can try reading it online, but I promise you the grammar and typeset will frustrate you. Instead check out their hostel recommendations and pick up a copy in the lobby. In person the maps are charming and quirky. The maps fold up easily to fit in your pocket and usually have the best, local low-down on where to eat, drink, party and stay. They even have a handy phrase guide. Handy phrases being "Who here would like to do a body shot with me?" or "Can you help me with my zipper?"
These things are obviously geared to the younger traveler, which makes them the perfect suplement to the Rick Steves guides.
So far Mr. Gordonsky covers Amsterdam, Barcelona, Berlin, Budapest, Krakow, Krumlov, Prague, Riga, Vilinius, Wein and Wroclaw. And I'm starting my own Boston one soon.
Perhaps with better grammar though.