At its most basic a text adventure puzzle takes the form of a locked door requiring a key, but what is there beyond this?
I'm a pansts writer (one who makes it up as they go along) and because of this I'm finding myself creating a lot of rooms that do little more than move the story forward and create a sense of place and atmosphere. I've got a couple of locked doors in there, but would like to get a bit more inventive and clever.
Anyway, fact is I'm looking for a bit of inspiration on the puzzle front before I wrap up my latest game.
It's going to be a horror, by the way, if that's any help.
I'd just recommend seeing examples of puzzles: playing/seeing/watching/reading-about lots of games with puzzles, and see all the different ideas/types of puzzles that others have already thought of and implemented into text-similar/like games.
Maniac Mansion (NES) and shadowgate (NES), and heck even Zelda 1 (NES) and Zelda 2 (NES), are good starts :D
Also, there's lots of SNES RPGs (and also the SNES 'Gaia' Series: Soul Blazer, Illusion of Gaia, Terranigma) with some really good puzzles... not sure how many can be translated into a text game... but maybe some can be so, or at least their concepts maybe....
there's also lots of the old computer games too with really good puzzles... Myst, The Dig, 7th Guest, 11th hour (sequal of 7th Guest), Indiana Jones, etc etc etc
Some types of puzzle that I like to work into my games:
misleads. The player tries to solve the wrong puzzle, and ends up accidentally solving the right ones. An example is getting past the college students in Detectiveland: (spoiler rot13'd) gurer'f n syntcbyr naq na bcra jvaqbj. Gur cynlre guvaxf gurl arrq gb pyvzo gur syntcbyr naq trg va gur jvaqbj (naq unf gb fbyir n fho-chmmyr gb znxr gur syntcbyr pyvzonoyr.) Npghnyyl gur jvaqbj vf gbb sne gb ernpu sebz gur gbc bs gur cbyr, ohg pyvzovat vg unf gur rssrpg bs nppvqragnyyl vairagvat gur 1920f snq sbe syntcbyr-fvggvat fb gur fghqragf nyy eha bss gb svaq gurve bja cbyrf, naq lbh pna pyvzo qbja naq jnyx va gb gur pbyyrtr.
wordplay. This fits some genres better than others. An example is the poker game in Draculaland, where (rot13) syhfuvat lbhe unaq bs pneqf qbja gur gbvyrg va gur eblny onguebbz genafsbezf vg vagb n "eblny syhfu".
chained actions/Rube Goldberg machines. The canonical example of this is the Babel Fish dispenser from Hitchhiker's Guide to the Galaxy, where you have to put the right junk in the right parts of the room to confuse the various cleaning robots - and you only find out about the next robot once you've got past the previous one. In my games I've tried to mimic this with the pizza puzzle in Detectiveland (rot13: fraq gur purs bss gb znxr lbhe cvmmn, gvr gur fcnturggv orgjrra gur punve yrtf juvyr ur'f bhg bs gur ebbz fb ur gevcf, NAQ znxr gur cvmmn rkgen fcvpl fb vg vapncnpvgngrf uvz), or the puzzle with Fraf and the mummy in Portcullis (qebc gur onananfxva ng gur gbc bs gur fgnvef fb ur snyyf qbja, naq nyfb bcra gur bira ng gur obggbz bs gur fgnvef fb ur trgf fghpx va vg - bgurejvfr ur'yy whfg eha onpx hc). These are fun to design and fun to play, since the player can see that they're getting a little closer to the solution with each step.
information, possibly coded like the gargoyles in Portcullis, or disguised as graffiti or an alien swearword, or just obtained by talking to the right NPC: lock combinations, addresses and so on. When I use these I like to randomise the code so that you can't just use knowledge from your last playthrough that it isn't logical for the current PC to know.
animals, especially when it involves the particular psychology or physiology of the animal rather than just bringing it a bone/fish/carrot. Example: the dog in Portcullis, which is pinning a wizard to the wall (rot13: vg'f fgnevat ng gur jvmneq'f fgnss, juvpu lbh unir gb gryy vg gb SRGPU.)
good old-fashioned locks and keys, or simple 'puzzles' that are the equivalent of them, like an NPC rewarding you for finding his lost macguffin.
put in alternative solutions where you can. Not everyone will think of everything. A good way of doing this is to get playtesters to send you transcripts, and if they tried any incorrect solutions that seem like they 'should' have worked, implement them.
And I'll second what hegemonkhan said: play puzzle games to get ideas. For a brilliant recent puzzle game I recommend Inside the Facility from this year's IFComp, which not only includes great puzzles of all sorts, it implements them with only six verbs required - the four cardinal directions, LOOK, and WAIT.
Hmmm... puzzles from Xanadu 2? Thanks for asking! =P
The end game set of puzzles is disabling six vehicles.
Also in X2,
A have a gazillion ideas for certain puzzles that can be used.
In X3, the first "smidge" of the game is all about collecting ingredients needed to cook a wrinkled, hungry, cranky, old man a chicken. My puzzles tend to be based on the combination of a lot of smaller events that each require smaller puzzles to complete. Games within games within games. =)
Shameless plug over
I like to do natural puzzles. For example, if you see a fire, try dousing it! Or if you see a place you can't reach, try moving a box or rolling a cart over to it so you can stand on it. Simple stuff like that. I also like variables affecting the outcome of puzzles like player intelligence, or player strength etc.