Puzzle and riddle goodness

I've been interested lately in incorporating some puzzles in my game. I know they can give the game a "funhouse" feel. But when I played I always enjoyed having at least one puzzle or riddle challenge in it (I guess they'd be seen as cliche now). I've been searching for some, and found I neat one derived from the Davinci Code on this site. I like the idea of using the Fibonacci sequence  (0,1,1,2,3,5,8,13,etc) but I worry because one of the players is also a math teacher and may pick up on it realy fast. My idea is to use pressure plates with stones on them where the adventures have to put the proper amount of stones on the last plate.
   I also have one which would be alot more challenging involving a geometric riddle which I'll paraphrase:

         A King wants his gardener to make plant 5 rows of 4 roses, only problem is he only has 10 roses to do it
    How what does he do?  I usually put a lot more flourish in the presentation when giving this one, but you get the idea.


Answer:  a star shape.

I also love old fashioned riddles too, but I find that sometimes they can slow things to a halt because if people can't get the answer, they can't progress any farther. So I like my riddles to be for non essentials (chests, scroll cases etc.). I also like how they were done in the old video game Betrayal at Krondor; where each riddle was given a dial lock mechanisms. (again Davinci Code did something similar for a scroll type case) I find they can make them a little too easy at times though, giving not only the possible letters but how many of them there are as well. Still, the right riddle can keep them challenging anyway, and we all know there are enough of them out there.

I also really like this idea from Die Hard 3 

That's all Ive got for now, I hope some of these are useful to you, and If you have some to you want to share please feel free.

See ya.