*bump* I'd like some recommendations as well.

I've tinkered with a bunch of map-making apps both free and commercial; they vary pretty widely in terms of capabilities and feature sets and, er... I mostly can't remember which was which :).  Most tend to lean toward fantasy, but in many cases there are modern and/or SF art sets that can be added to them. There tend to be separate choices for regional/geographical maps as opposed to indoor/"dungeon" layout as well.

The big three for me in terms of geographical mapping would be:

• Campaign cartographer 3:  Amazingly flexible with the most available plug-ins and add-ons... but with a price and learning curve to match
• Inkarnate - Much more simplistic in comparison to CC3, but you can still do a lot with it.  Has a free version and a paid version - this is where I'd probably start just to get a feel for it.
• WonderDraft - Falls somewhere in between the above 2 in terms of features and price.  This is the one I ended up going with maps to accompany some writing and a D&D campaign, mainly because it happened to have a couple of built-in styles that worked well for what I was doing

Honestly for MP I haven't bothered with this kind of map.  My campaign is set in a modern-world analog with cars and planes and helicopters and GPS, so unless the players are venturing out into the wilderness or have ended up off-world somewhere, the ability to find and get to the place where the action is happening is sort of a given.

There are also some tools better suited for floor plans - dungeons, buildings, caves, etc.  I tinkered with a few of them as well, but found that generally they didn't add much over just a rough sketch of an area in my notes.

Roll20 maintains a list that I think is a little out of date / incomplete, but might be a decent place to start:  https://wiki.roll20.net/Useful_links_for_mapping