I've done approximately three trades in my HeartGold, and in SoulSilver, I did only one. HeartGold—the first trade was with a guy at the fifth floor of Goldenrod Department Store. He offered a Machop for my Drowzee, and I accepted. (: This Machop was Adamant, and it had the No Guard ability. That, if you ask me, is a great combination! Adamant powers-up its physical attack stat, which it specializes in. With No Guard, this Pokémon's got the chance to hit any move without worrying about its accuracy—DynamicPunch, Stone Edge, ThunderPunch, Ice Punch, you name it. Its nickname was "Muscle," though, which I didn't really like. On my second trade, I've swapped my Dugtrio with a Magneton. Magneton was holding a Metal Coat, which is a very rare item. Finally, during my third trade, I have exchanged my Pikachu with the Pikachu of Lt. Surge's. xD I've found his Pikachu to be quite special, as it was owned by a gym leader. Not only that, it also had a great nature: Timid! Pikachu is quite speedy, and Timid helps it become even faster.
In Pokémon SoulSilver, I've traded my Rattata for the Steelix of Jasmine. I would've given her some other Pokémon, but… y'know. I just didn't have anything good. Well, I did, but they were all a part of my team, and I wasn't ready to let any of them go yet. D: After getting a hold of this Pokémon, I've used it for only two - three online battles, I think, and put it into my PC box after that. To be honest, I felt a little sad for taking Steelix away from her. If she wanted it back, though, then I would have given it to her in a heartbeat!