The subject of definition of Coordinate Reference Systems is quite complex and sometimes confusing task.
To simplify usage of MapTiler application I prepared a list of Coordinates Systems sorted by area of use. Typically users know only the name of the CRS for their map, but not the exact definition (parameters of the datum, used map projection etc.).
Most of the geodata formats (like GeoTIFF) contains the definition of the Coordinate Reference System already - then it is used by MapTiler automatically.
But sometimes the embedded definition is missing or does not describe well the transformation.
An excellent online tools for simple search in the database of available coordinate systems: http://www.spatialreference.org/,
You can try to find the EPSG code for your input map in the official list. The complete list of definitions is online in EPSG database, search is here: http://www.epsg-registry.org/.
In case you have problem to find the EPSG code, or it does not run in MapTiler, you can try to find your coordinate system definition on this website and just copy&paste the WKT into MapTiler window. I am adding here the very frequent systems and also the problematic one:
Inspiration by another list. (I am going to add more coordinate systems into this list as people will use it).
If you are not familiar with this subject I recommend you to have a look at: Geometric Aspects of Mapping
Interesting source of information is also: Map Projections, Gallery of Map Projections, Proj.4 documentation
Excellent source of information are also Mugnier's articles: http://www.asprs.org/a/resources/grids/
I am providing consultancy. Feel free to contact me, look at http://www.maptiler.com/