Finally Time For A New Fish... Stocking Ideas?

[simonero]

I finally have motivation and justification to get a new fish!  Woohoo!  Only problem is that I have no idea what I want..  especially not for this sized tank.
 
The tank is 20gal long, well-established, sand substrate, and currently houses 1 adult canas apple snail, 2 albino mystery snails, and infiniti trumpets.  It is lightly planted with java moss that miraculously grows faster than my apple snail eats, but otherwise will not be planted.  
 
Ideally I'd like a 1-fish oddball species tank, so it only needs to be peaceful enough to leave my apple snail and mystery snails alone (i.e. no puffers!).  I'd rather have a larger fish than a more active fish, as a trade-off given the small tank size.  But I'm open to suggestions.  Nothing unusually sensitive to water fluctuations, must be average/normal to hardy.
 
Alright..... so who can think of a fun oddball for my tank?!  

 

[Munroco]

What about one of the medium size cichlids. They have a bit of personality. I don't think they would bother snails, but I'm open to correction.

 

[attibones]

Peacock gudgeons! You said you wanted a single fish due to tank size, but a group of gudgeons would thrive in a twenty gallon (and probably breed). They are absolutely fantastic fish. I loved mine. 

 

[simonero]

Cichlids have never seemed like much of an oddball to me >.<
 
The gudgeons are also cute but I don't want a school!  I actually just stepped away from a year-long guppy breeding situation heh, I'm more-so looking for a single, interesting fish (or very small group potentially [max 3]) that won't exponentially increase in bioload or require me to use them as stock or give them away to maintain my bioload!
 
Any other ideas?