Text games

You are likely to be eaten by a grue. - Zork.

Amnesia: The Dark Descent?

Analogue: A Hate Story, also the sequel is coming soon (Hate Plus).

Does Hacker Evolution / Uplink counts as text-based? :)

The text adventure in Moonbase Alpha will give you a good challenge.

If you can find it, The Hitchhiker's Guide to the Galaxy

I haven't played that many IF games, but my favourite text adventure game is Enemies by Andy Phillips. Some reviews. It's a psychothriller or mystery/horror game.

You can download it here.

It's pretty difficult and prepare to die a few times, but I liked the plot and puzzles.

Text-based you say? :)

Well these are more visual novels but Dont Take It Personally Babe It Just Aint Your Story, Analogue: A hate story, and Digital: A Love Story were all good ones to me. Two out of the three being free.

Last text based game I played was Realms of Despair, a MUD. Before that, Moria on the Amiga. :D

Recently, I have also found this one:
http://adarkroom.doublespeakgames.com/
Looks quite interesting :P

zork

http://www.gog.com/game/the_zork_anthology

Clicky.

The Lurking Horror another IF game

Just for shits and giggles I will say Corruption of Champions... Warning SUUUUUPER NSFW.

visual novels based on branching paths are mostly text basedof course

What do you mean text based?

Space Rangers 2. Very nice text quests.

I remember reading about "XXI century text adventure" Cypher some time ago, but never played it myself. Maybe it will interest you: http://www.cabrerabrothers.com/

Torn.com

Ib?

http://www.aardwolf.com/