Here I offer you two maps for OpenTTD that I have created myself, and a scenario which I didn't make, but is no longer downloadable on the official server. It is recommended to update to at least 1.6.1.
All the maps listed here have one thing in common - a rough and diverse terrain. In my opinion, automatically generated maps offer too much open space and too few obstacles, so nothing prevents you to simply repeat the same patterns all over the map. The game quickly becomes boring when you don't have to improvise and solve new problems.
Industrial Land (March 2014)
This mapy is very tiny (1282), but "finishing" it will be difficult nevertheless. It is an experimental map - the point is that all industry is concentrated in one corner of the map, where you can also find large cities, while all resources are scattered across the map. The northern part of the map is divided by rivers, while the southern part is mountainous. Construction of railways from mines to industry certainly won't be easy, but the biggest problem will be to build a very busy complex in the industrial region.
You can notice the German town names - the map is very loosely inspired by Germany, but doesn't aim to be geographically correct at all.
Alpine (October 2018)
Because I found the concept of Industrial Land interesting, I decided to create a more ambitious project - same principles, but 16 times bigger map (5122), which is once again loosely inspired by real world, this time it is the southern Alps and northern Italy. It is not geologically correct either - in these Alps you can find deposits of coal, oil and iron ore and the most productive mines are found in higher altitudes.
That means you'll have to funnel trains from all corners of the map through narrow valleys and choose a compromise between elevation and length. Most of the industry (except sawmills) is concentrated in northern Italy, where you'll have to build complicated, high-flow interchanges in confined spaces.
In October 2018 I did a major overhaul - most importantly, I added the Apennine peninsula, so the geography is now a little bit more realistic. There is a very small chance of instability though, so please leave me a comment if you experience a crash. Here you can download the old version (December 2016)
Dinora Islands, created by Michael "Bot_40" Rippon
This map was one of the first I ever played and I consider it to be excellent - it is well balanced and the difficulty is just right for a beginner.
Dinora Islands is an archipelago, where you'll have to choose the right positions for bridges, while inland hills force you to save space. Thanks to the diverse terrain you are guaranteed to have lots of fun despite its small size (2562).