I stoled your 'mon, man.

[Drago]

Though I initially was thinking of this topic with regards the GTS, I thought I may as well branch it out to all the games. Here, we all recall and celebrate the most spectacularly one-sided trades we've ever made. Mine will all be GTS related, 'coz it seems like it's easy to rip people off there.

How long has it been since I've actually caught a Pokemon? It's been a fair while actually; I pretty much stopped, far more content to pimp out a couple over the GTS for whatever I please.
Here's a tip for anyone who wants to use the GTS. Breed lots of Eevees. Lots and lots and lots. Why? Because they're still as wildly popular as ever, and some people don't seem to realise you can get one for free after you've gotten the National 'dex. I've had a bit of success with Murkrow and Elekid as well, but trust me, Eevee is the best I've found for this.

To first test this theory, I offered a freshly hatched female Eevee in exchange for a Spiritomb, since I've never managed to catch anyone underground. I left it for a couple days, came back, and bam, lv.25 Spiritomb, caught with a Master Ball, had been sent my way. So I went for the big one, and in a move I still can't quite fathom, I made the most one-sided trade I'd ever managed.

Eevee for Dialga. No way that would work, right?
...Wrong. MALE Eevee, newly hatched, sent off for a week. And when I came back, there it was. A Master Ball-dwelling Dialga, adamant orb attached, at level 100. So can anyone explain this to me, other than people really love Eevees?

And feel free to see if you can top that little swindle. ;)

[Austrian ViceMaster Alex]

I've only done a single trade so far on the GTS. And guess what I wanted? It's an Eevee! After all there are seven Eeveelutions, so to catch 'em all I need seven Eevees.

I figured the starter Pokémon are always wanted so I just started up a new game of Pearl, got myself that silly fire monkey (I hate monkeys :P ) and as soon as possible put it up for trade after transferring it over to Diamond. The next day I had a new Eevee - awful stats and everything but it was good enough to fill up my Dex.

I think it was a good trade, trade a Pokémon you get in 5 minutes for one that you need to play for 25 hours to finally get.

[AntiAsh Superstar]

Nyahaha, I really ought to see if I can blag something like this, I've seriously loads of spare male Eevees after I was trying for several days to breed a female. :O If they're so in demand I could make a killing!

I do guess it's got something to do with their multiple evolutions tho, you're gonna need seven as Alex has already said and not everyone has the patience I displayed to get my full set of Eeveelutions. :3

[classy_cat18]

I don't really get those one-sided trades, although I don't really use the legendaries other than to fill up my Pokedex. But I deposited a male Elekid with an Electrilizer (sp?) and asked for a female Eevee. Twenty minutes later, female Eevee at level 1!

[Crystalmaster Mike]

Well, I suppose it could be easy to explain if your Dialga turns out to have 999 for all stats, or all-round 31 IV's...

But I don't really recall many one-side trades... Other than with myself, of course. You don't really go through all the troubles of doing the Mew Glitch on Red, filling your 'Dex, to trade over your level 100 Foobar from Silver. Nah, you trade over a spare 'karp or something, or a double (God bless the Box Glitch!).

[AdventureSerum]

People will trade ANYTHING for Spiritombs and Beldums. Which is convenient, being that I have about 300 Beldums right now. Breed the crap out of a currently level 98 Beldum, fill up my Pokedex. Works great.

[Austrian ViceMaster Alex]

Hm, what I'm really looking for right now are Latias and Latios. Eventhough I have completed the generation three games where they appear those pesky buggers never show up even after hours of hunting. So if anyone wants to trade those, I'm game. We could trade for a ... Beldum, for example. ;)

[Darth Cookie Monster]

I think that because eevee has so many Evolved forms, people want many eevees for battling. That and to breed attacks on to other eevees and other pokemon

Darth Cookie Monster

[Dark Scizor]

If Austrian Vicemaster is around, I could trade you a Latios or Latias.

I've got Pokésav, so it's nothing to me, and I can make them rather legit.

[AdventureSerum]

I could use both those two...

[Austrian ViceMaster Alex]

Don't need them anymore, thanks for the offer though. I almost got my Pokédex completed by trading people a hole hoard of Houndour. They seem so popular I can get almost anything for them. It seems they are relatively rare and so I can trade them even to Pokémon I usually could easily get. So they are bad trades for me ... but I'm just lazy.