I run Dungeons & Dragons games with Roll20, a great “virtual tabletop” (VTT) app. It lets you upload image files to use as a map, for exploration or combat. You put tokens for your player characters, and any NPCs and monsters you like, on the map, and all the other players can see what's going on, move their characters around, etc.
(There are many other VTT apps out there; I just happen to like Roll20.)
In this part of the site, I post maps of various dungeons that are ready for use with Roll20. Most of the maps are from published adventure modules (by TSR, Wizards of the Coast, or other publishers). Some are my own creations. (See the introduction for an explanation of why you’d need a re-done version of an existing map in a published module!)
All of the maps are available in multiple resolutions and formats, and all are free for download. Happy gaming!