Most of the tiles that produce anything can have the quantity doubled or trebled by application of the appropriate technology with the appropriate civilian specialist. Scrub forest is the exception: just one unit of timber for ever.
Mountains can be among the most lucrative of the tiles in anyone's empire, because some produce treasures such as gold or gems (with or without less exciting minerals).
Terrain has an effect on one's ability to construct railroads (and in Imperialism 2 initially roads). Details differ between the games.