Aerial photos, contour maps, topographic maps, any map I can get my hands on. I try to learn the areas the locals have names for and correspond those back to the maps - so look at fishing reports and maps together. I have a couple GPS synced sites for maps so i can get coordinates right from the map and then I plug them into the lowrance via SD card. Maps, maps, maps, and then some more maps. Arial photos from bing, mapquest, google all can be different and give you ideas - you can often see emergent vegetation, current breaks, etc. right from the photos.
D