Parkopedia is aptly named — its database contains locations, and often pricing and other details, on 15 million parking spaces in 20 countries. So if you need to make a list of three go-to parking spots for a trip, it's a great place to start.
Parkopedia covers private, tag-needed parking, public garages, free street parking and meters, and offers a very smooth and smart use of Google Maps. Click on any parking spot, and you'll see details if they're available, along with tabs to get directions, see a Street View of the spot, and reviews, if other Parkopedia users have left them. If you've got a certain price you want to pay for a certain day you'll be parking, you might find the spot with Parkopedia's sorting function. It's free to use, and there's an iPhone app and mobile-friendly web app, with more native apps on the way.