Substitute for horseradish? What are some good substitutes for horseradish?

I've heard mustard is one, but I still struggle a bit to see how it would do a very good job...


Anybody ever try mustard with success?


I've also seen online that some people suggest wasabi, but let's be honest, the "wasabi" that most of us are familiar with is actually horseradish. 

(Oh, and please don't suggest horseradish sauce -_- . That one is obvious).  



Update:

I like horseradish, but horseradish is not available at my local market. 

I'm just trying to achieve the same sharp/pungent "kick" that horseradish typically brings. The flavor is almost immaterial; I just want the "kick". 


As such, I'm not particular to trying it in any specific dish. I'm just curious what other foods can produce a similar feeling/tasting "kick" as horseradish.


Note: Wasabi is also not available at my local market.
Mustard can be used, but it might have a lot of vinegar in it and can clash with whatever you are doing.

Maybe try doing something with mustard powder instead of prepared mustared.

You could try, if you are luck to get some real fresh Wasabi roots; that would be close to the perfect substitution.