My Mapping Needs
Since I play primarily online at roll20.org, I have need for clear electronic maps that let my players know exactly where they stand, without usurping the role that DM descriptions should play in their imaginations.
Making My Own Maps
The most important tool I use is GIMP. GIMP is a Photoshop-like image editor. It's open source and free as can be. It's also complex and has a rather steep learning curve.
Indoor Maps: The far-and-away best mapping community on the internet can be found at The Cartographers Guild. I could probably fill several pages with the excellent tutorials and scripts available on this site, but one GIMP script in particular stands out as my go-to dungeon mapping solution: site administrator RobA's Subterrainian Map Prettier Script--an understatement if there ever was one! The thing takes a black and white doodle and turns it into a ready-to-run dungeon, all in the time it takes to have another gulp of coffee.
Outdoor Maps: Outdoor maps have fundamentally different requirements than indoor ones. Dungeons are made of walls and doors. On the other hand, the Great Outdoors is made of many different kinds of terrain which need to be easily and clearly represented. For this purpose, I usually rely on the GIMP overland brushes found at vintyri. I also sometimes google up my own images and use them as a quick-and-dirty way to get the right color at the right spot.
Objects: For either indoor or outdoor objects, I usually google the dundjinni site--yes, dundjinni.com shut down awhile back, but their forums are still up and jam-packed with all the map art goodness that has been uploaded over the years. Other great sources include Vintyri and rptools.net.
Labels: Deserving of its own section because it's so goddamn important for me as a GM to be able to see which areas of the map I have keyed. I recommend and use RobA's Label Points Script. Save it as its own transparency and put it on the GM's layer in roll20. Easy as pie.
Using Other People's Maps
Plenty of places out there have their own collections of pre-made maps. The Cartographer's Guild. Dundjinni. Dyson's Delves.
I'll try to keep this section updated as I stumble across new resources in my planning.