9) The weaker Legendary Pokemon
For those of you like me you may be wondering why an elegant blue serpent dragon evolves into Barney's retarded cousin. A Mega evolution may be the perfect way to fix this, make him more like his previous forms while still retaining the appearance of an evolution. Plus if you look at the evolutionary line for this guy, he would be perfect to combine the dragon and fairy types, making a dragon that Jigglypuff cannot destroy.
7) Any Bird Type
6) Porygon Z
5) Snorlax & Sudowoodo
The reason I picked these two is simple, there's not a lot of them, usually just 1 or 2 in each generation. This means you usually had 1 shot to catch them or else you could never finish your Pokedex. In fact up until a year ago my brother was convinced they were legendary Pokemon because of how rare they seemed to be in the games. Alithough if I had to choose 1, then I'd go with Snorlax just because the thing is so cool.
4) Pokemon that Don't evolve
3) The rest of the trade evolvers
1) The Rest of the Starters
In X and Y we get a new starter, one that I really liked, but then I got a Torchic from Mystery Gift, and then a Charmander from the Prof, and guess what: those two Mega evolve. Thus my new starter ended up taking a backseat because he simply couldn't compete. The starters are the Pokemon that you choose at the beginning of any Pokemon game and are supposed to be your partner throughout your journey. With that logic it only makes sense that they ALL get a new form that is based on the personal bond you have with a Pokemon (at least that's how Mega Evolution is explained in the games). I chose to start with Fennekin, and in doing so screwed myself with a massive water weakness by having 3 different fire type starters, so why make it worse by making Delphox a weaker option than the others.
Agree with my list? disagree? feel free to leave a comment below, I'm interested to hear what Pokemon you all feel deserve Mega evolutions.