heres one i use mapper
heres a few pictures of what it makes, these are very simple pics
throw the randomly generated map into paint, gimp or paint.net or whatever you want to use and add a few things. works well for me, plus its free.
for paid options there is also campaign cartographer or fractal mapper i got fractal mapper for about $60 i think
Gimp is free and similar to Photoshop. Check out Cartographer's Guild for some tutorials to get you started. This is the cheap solution, but requires work. I think Campaign Cartographer's city add-on does good stuff if you want easier but more expensive.
http://www.cartographersguild.com
You can also just use Maptools to make maps. There are tons of libraries you can download that contain all of the tokens, objects, backgrounds, etc you need to make excellent maps.
Inkwell Ideas has a cool random city generator that is usually at least a decent place to start for city design. It's very basic, and of course random, but free. You can always start by generating a city with it and then importing the image to the GIMP for touch up and additions.
Apparently they've also just had a successful kickstarter for "Cityographer" which is in the same vein as their Dungeonographer and Hexographer programs, which run about $25. So if you wait awhile there's that as an option too for city design.
Following up on what mearrin69 said, Campaign Cartographer is $45 and its City Designer add on is $39.95. It's a great program--extremely powerful, which is what you're paying for there (from what I understand it's actually cheap, relatively speaking, considering it's based on the CAD engine). But not on the cheap/free side. What I'd suggest is finding your free alternatives (including drawing straight into the GIMP; some if not most of the best mappers just use GIMP or Photoshop), and later if you get some money to burn and want to really dive into massive world building, go to CC3 and buy their "world builder bundle" which is CC3, Dungeon Designer, City Designer, and Fractal Terrains for $148.
ETA: I should also note though that if you really get into just CC3 and learn it inside out and are cool with making or importing your own artwork, you can pretty much design anything you want with just CC3 without any of the add ons. The other add ons make it much easier but are not strictly required.
Cool, glad to hear it. That site really is a useful resource.