I'm going to list most memorable from each year, since I have a LOT of favorites.
2006: In a CTF hidden-flag soakfest, I unloaded an entire CPS 2000 PC into someone who wasn't even looking at me.
2007: In a 1HK game, while walking down a line of tall shrubs, I nailed an opponent with a Max-D 3000 (who was within 5-10 feet), the only time I remember getting a very clean/obvious pistol kill. (It was easier to wield there than my CPS 10k.) He was a very good sport and didn't even fire back at me which could've caused confusion as to who hit who first.
2008: Hit a shield-blaster user in the lower leg/foot during a 1HK game. He cheated and didn't count it.
2009: Got a dual wield kill in a "light blasters only" (per my definition) FFA 1HK round. I had a pair of Max-D 3000's.
2010: Nothing real memorable as far as my kills go, except a lot of hilarious riot shield action in CTF 1H(team)S. In one game, the other team took the longer hose to their advantage, and attacked my whole base with it along with a sled shield.
2011: Two memorable kills in 2 days of water warfare. Both in 1HK.
- Hit an opponent with a water balloon + CPS 12k tap shot series combo-attack. (The water balloon exploded in his hand when he tried to catch it.)
- Stalked same opponent, sneaked up to a building's tall wall, nailed him with an XP 270 by complete surprise when he returned to his hiding spot.
2012: Sneaked around a house (not my house) and shot an opponent in the back in a 1HK game.
- Hit SEAL twice in the 3-lives assault round.
- Pretty much any hit I got on Scott for the whole weekend.
- Charging against Marauder with a 10k while he had a 275.
- Charging against Latsvyert in the BBT-only game.
- Getting a long distance hit on Duxburian in the BBT-only game.
Sorry, but I couldn't pick a favorite out of all these.