Spike’s a supporting character so its support.

Power of brave

@Jarkes  
No, KUSHLiNiBAlAr.

@Background Pony #3C98  
DRAGON’S BLOOD!!!

The element of Sacrifice

@Deserter  
Oh, it can get much higher, it just takes one guy really. One guy who wants to spam the comment thread.

@Katastrof  
Oh, come on, it’s only 87 comments, I seen bigger threads.

Stop comment this. I can’t hear my own thoughts from that high.  

@Villain Pony
 
“PUSHLNBAA?”

Carbon, for diamonds

Potassium.  
Uranium.  
Sulfur.  
Hydrogen.  
Lithium.  
Nickel.  
Boron.  
Aluminum.  
Argon.

Perseverance

Element of Helpfulness

Forgiveness? I mean, it’s still an Element of Friendship. Since it’s inevitable you’re gonna get one of those topics where you start ripping into each other and then decide it’s not worth continuing the argument and it’s more important to keep being buds.

Faith.  
Like so many of the other elements of harmony it is simultaneously something he represents and needs to work on. (Ex. Rarity being both extremely generous and somewhat greedy).  
Spike has extreme faith in others. He never gives up believing in Twilight or any of his friends really. But he lacks faith in himself, as demonstrated in the newest season with his self confidence issues. He will never stop having faith in his friends and believing that they can do anything. At the same time, he believes himself to be unworthy at best and a greed obsessed monster at worst.  
So since faith is something that he both represents in some regards and lacks in others, I think it would be the best element for him.

@Background Pony #E355
 
I’ve actually always figured that Shining Armor and Cadance both represent the Element of Love…

Strength.

@dekutree64  
Oh, good! There’s going to be one for Flash Sentry, the Element of Love… and maybe one for Spike.

@ED-SKaR  
Nah, only British English has the superfluous u. Even Latin spells it “honor”.
 
@Psychopomf  
Exactly :) The little bits of harpsichord music in Spike At Your Service, and his fantasy in Dog and Pony Show, all point toward him being an inversion of the typical dragon-slaying knight.
 
But even aside from that, here’s a forum post from a while back comparing the Tree of Harmony to the Kabbalistic Tree of Life: http://mlpforums.com/topic/97291-the-kingdom-and-the-tree/
 
As said there, my theory is that the 8 pointed stars all over Twilight’s castle mean that there will be two new elements discovered next season… and one of the as-yet unused spots on the Tree of Life diagram just happens to be Honor :)

Courage. Totally.

Strontium.
 
Because that’s the first element I thought of.

Heart.

The element of humdrum…
 
 
Ahem, on a serious note, I really like the comments about “hope” and “Honour”, those two really fit him.
 
@MasterSpike
 
@Q.E.
 
 
PS, Honour has a u in it, all y’all can’t spell.

patience

Enthusiasm? X3