Tools You Can Use
Pencil and PaperNothing beats the rustic and organic feel of hunkering down and cracking out a pencil and paper and drawing a map for yourself. It's actually a wonderful tool for getting the creative juices flowing and you have literally no limit except the borders of the paper. However there are a couple issues with this; for one, humans aren't perfect. Chances are you're going to make mistakes and your map can only take so many eraser stains. If you're an artist, drawing a map could be a cheap, fun breeze. But if you're like me, and your hand-drawn maps looks like something a kindergartner could think up, basically an amoeba with rivers scarring its surface... Well, this may not be the best of options.
Coastlines and fractal-like natural features that really bring a map to life can be hard to emulate as well. Of course, there are some solutions for this. One creative thing I've seen is to take small objects, like beans for example, and scatter them on your page. Clump them and arrange them however you wish. Then take your pencil and trace around the edges of the clumps of beans; this well create a random and rugged-looking coastline, possibly with some islands nearby!
Online ToolsIf you're a bad artist with a tight budget; fret not! There are still plenty of computer-aided tools that are 100% free at your disposal if you know where to look. However no online tool has all of the freedom that drawing your own map does, but they can really help to inspire some creativity if you're looking for some.
Azgaar's Fantasy Map GeneratorThis is a powerful tool, if you know how to use it. This tool generates countries, cities, rivers, heightmaps, and more recently, biomes and rainfall maps. Almost every aspect of this program is editable, giving you immense flexibility and, honestly, a rabbit hole to fall down. What's great about this tool is that it is updated from time to time to include more features and fix bugs, so I recommend always coming back to it to check for updated versions!
Inkarnate (May be picky depending on your browser)
Inkarnate is a wonderful, free, online tool that only requires account creation to utilize. With this tool, you start with a blank canvas of open ocean and can add land to your heart's content; after this, you can add terrain contours and then some images such as trees, mountains, markers, and text to bring it to life. The biggest downfall of this tool, however, is that land-shaping is quite hard. You are forced to choose between circular of hex brushes when painting land/sea, and the size of the brush. It's hard to paint a pretty coastline unless you use very small brushes and take your time sculpting the coast inch by inch. Also, as far as I know, there is no "river" tool, and rivers must be crafted by hand, by "deleting" a thin sliver of land with the brush tool turning it into water and trying to make it look nice. I gotta say though, this effort can really make the map look great if you take your time and focus with the coast and rivers. After that, the rest is cake.
DonjonThis site is
awesome y'all. This link will take you to a fractal world map generator, which, when given some starting parameters and a randomizing seed number, will generate a gorgeous world map that looks pretty damn real. The site is also filled with all kinds of other fantasy world tools, like demographic/dungeon/name generators, and more. As a bit of warning, this is the "fractal world generator." On the site, there is a "fantasy world generator" that is quite similar to this tool. However, the "fantasy world generator" often crashes and leads to an error page and only works a fraction of the time for very little benefit over the regular "fractal world generator."
Mewo2This is a little-known map generating er... demo thing I found. The controls of it are a little odd and I don't understand 97% of the code talk that the author is explaining, but it's certainly worth toying around with and seeing what kind of results you get. This tool is especially good at fractal erosion, creating long, winding rivers, and placing cities in logical locations on the map. A strategy I used to use with this is create a map here, but then use it as a model to recreate and bring it to life with another tool like Inkarnate.
Paid SoftwareWe often don't want to pay for things nowadays, but the general rule is that if you pay for something you get more in return. So pay-to-use mapmaking software is something worth including here.
PhotoshopPhotoshop is basically like MS Paint but so much more powerful. I've personally never used Photoshop to create a map but it's definitely possible. Try searching YouTube for some helpful tutorials on how to use this application to create fantasy maps; there are many methods for doing so. I would recommend using a tablet with this software as using your mouse at this level would probably be quite tedious.
Fractal Terrains 3 (Link won't work in Chrome, I think.)
FF3 is an
amazing software. At the touch of a button, it generates entire worlds before your eyes. The damn program even generates climate, rainfall, altitude, and temperature data. You can add textured climate overlays and a cloud overlay to basically make the map look like a satellite image. The app can even generate realistic rivers based on rainfall and altitude gradients. If you don't like the world in front of you, you can edit it yourself or generate a completely new one. The major downfall to this app is despite how powerful it is, generating worlds is all it does. You CAN'T add cities or label it... As far as I know. Hell, even if you're not worldbuilding, it's just fun to play with!
Campaign Cartographer 3 (Also won't work in Chrome, I believe.)
Made by the same company as FF3, CC3 offers basically everything that FF3 doesn't. In CC3, you can draw maps, add and label cities with beautiful artwork... The best news is that FF3 can export its map into CC3; so if you have both, you literally have the best of both worlds. If done right, you can make some amazing maps with this software. It is easy to learn, but impossible to master though, so I'd recommend googling some tutorials on how to fully utilize it.