Mewtwo - Psy-Clone: Should be obvious. It's a
psychic
clone 
Also a clever spin-off of the word cyclone. And I like clever nicknames
Moltres - Io: The volcanic moon of Jupiter, and the only volcanic moon currently known. Signifies uniqueness and strength, which is what I'm aiming for.
Lickitung - Carnation: It's a female, and thus, I decided to name it something involving the word pink. Carnation works well for that.
Unown C - Curiosity: I tend to name my Unowns after a quality in a person, such as my Unown S, Secrecy. Curiosity, though, is fully EV Trained, and it has HP Fighting with a +Attack Nature. I thought it deserved a special name.
Glalie - Voor-mhass: The name's something of a spin-off of the name Voor-hees, god of something-or-other(Sike Sanr suggested that name for Glalie). But I actually didn't name it with Voor-hees in mind. It actually came out unintentionally 0_0 It just occurred to me one day, and I figured that since I had a Modest Snorunt I could train, why not? So I did. Voor-mhass will have a counterpart, an Adamant physical Female Glalie named Viir-maess. And then the two shall breed to create a mixed Sweeper

Its name hasn't been determined yet, but I think Cryo would be a cool name(suffix meaning Ice).
Hitmonchan - Jackjumper: This is one of my more clever nicknames, IMO. Since Hitmonchan's English name is based off of Jackie Chan, I wanted something involving Jackie or Chan in its name. Chan really didn't work at all, so I focused on Jackie. When the shortened version, Jack, came into my mind, I somehow linked that with the deadly ant of Australia, the jackjumper. Jackjumpers are swift, fierce, and they hit hard. Just like my Hitmonchan. So, I named Hitmonchan Jackjumper to symbolize speed and power(jackjumper), and adeptness at physical strength(Jackie Chan).
Minun - Difference: My soon-to-be Modest HP [Ice/Grass] Minun. I'm working on hatching it in Emerald, with limited results thus far. But when I get it right, I'll begin working on Sum, who, as you might guess, will be a Plusle. Sum will be Timid, and his Hidden Power will be the opposite of Difference's. In battle, their Abilities will power each other up, and they'll be my main Double Battling force.
Some future nicknames I have in mind for future Pokémon are Atlantic the Kyogre, Skulkraken the Gyarados, and Pyre the Charizard. Atlantic because it's a great song by Thrice and fits Kyogre's vast image, Skulkraken because that was originally going to be Gyarados's English name, and Pyre because it's a non-cliché name involving fire(I might add on some word that involves air, though, to note on Charizard's other Type).
I only give nicknames to my most important Pokémon. The ones above are Pokémon I worked on getting for days and days, and I want them all to have good names. Psy-Clone's significance is a Timid Nature, correct EVs, and a BoltBeam/Recover/Calm Mind moveset. Io's significance is that it is Modest, has HP Ice, and has Substitute. I haven't trained it yet, but I plan to soon. Carnation is Adamant, has proper EVs, and its MS is Shadow Ball/Swords Dance/Return/Brick Break. Curiosity has a Choice Band, is Naughty, has HP Fighting, and, again, proper EVs. Glalie is Modest, and its MS is Water Pulse(to be replaced with HP Special)/Ice Beam/Crunch/Substitute. Jackjumper is Hasty and has HP Ghost/Sky Uppercut/Earthquake/Rock Slide. Difference and Sum have been explained.
Overly-long post, yeah, but I tend to overdo things like that >=P
Okashira: I like those nicknames, perhaps because I know what they mean xD Daemon is an awesome name for Houndoom, considering it
is something of a demon.
~*CB*~
The 8th Champion