This list is not a recommendation of languages that you should learn or use (see  for that. The majority of the languages on this list are languages that i don't know but want to learn.
Please note that my intention here is not to be comprehensive (see http://en.wikipedia.org/wiki/Template:Programming_language_lists if you want that), but rather to list only those languages that i consider to be of particular interest. 'Of interest' usually means that either this is one of my favorite languages to use, or that i think that a language has something to teach about programming language design (which has not yet been generally absorbed, e.g. i've heard that Lisp invented if-then-else, but by now everybody is familiar with that construct), or that i want to learn it.
- Scripting languages
- Languages noted for their object model
- Languages noted for their concurrency
- Data languages
- System programming languages
- Languages notes for their extensibility or flexibility
- Functional languages
- Flexible/powerful type systems
- Dependently typed languages
- Mainstream languages (remember, not a comprehensive list!)
- by "mainstream" i guess i mean things like imperative eager OOP with mutable variables, function calls that look like f(x,y), etc
- Array languages
- Stack languages
- Micro languages a la Jonathan Wright (http://www.acooke.org/cute/GoRocksHow0.html)
Some books and links to learn about these languages
As above, these are mostly things i want to read, not things i've read.
Important languages of historical interest
see also http://en.wikipedia.org/wiki/Generational_list_of_programming_languages