The
Interactive Fiction Archive has a massive library of text adventures. Depending on what format you choose, you may need to download certain programs (such as Windows Frotz) to run them.
Since the sheer volume of text adventures there is probably a bit overwhelming, I'll highlight a few:
Anchorhead: If you like Lovecraftian horror, this is a pretty solid entry in the genre.
Spider and Web: A spy-thriller told through flashbacks. Your character is strapped to an interrogation chair and is slowly reconstructing how they got there. I haven't played past the intro scene yet, but this one comes highly recommended by most people I've talked to about it.
Adventure: Colossal Cave: One of the early all-time classics in the genre. The puzzles are hardly intuitive, especially by modern standards, but it's a fun diversion, and a lot of early adventure games make references to it.
Slouching Towards Bedlam: Another game I haven't played, but have heard highly recommended. I think it's supposed to have a slight steampunk pastiche and some meaningful character choice options.
Finally, if you want to try your hand at writing some of your own text adventures, I highly recommend
Inform 7. It uses a natural language coding system that takes a bit of getting used to, but once you're familiar with it, you can just write things like "The kitchen is a room. Bob is a person in the kitchen. Bob is wearing pants and the propeller beanie" and the engine will understand this and create all the appropriate rooms, objects, etc. The only thing I have found that Inform 7 is not very good with is tracking stats, should you want to use any, since you have to "describe" any math you want it to do in full sentences. I haven't used it in a long time, though, and it's possible that subsequent updates have improved this.