I had a hard time deciding between Nasty Plot and Swords Dance on the poll; I like them both.
Some of my other favourite attacks are:
-Curse (the Ghost version). I find it to be very useful against trainers who are down to their last Pokemon, or on a Pokemon that has used Ingrain. Plus I just find it to be a wonderfully evil attack. I once created a fakemon that specialised in using this attack. She was a Mismagius evo, and my favourite of all my fakemon.
-Thief. I just love stealing items from other Pokemon. For some reason I like it better than Covet; maybe it's because I'm not fond of begging, or maybe it's because Covet can't be used on a ghost Pokemon. Maybe it's because my favourite character to use in RPGs is a thief. I also find that far more Pokemon can learn Thief than Covet (plus, it's a TM move).
-Metronome. This is probably my top-favourite attack, and I keep it on practically every Pokemon that can learn it. Sometimes I get interesting attacks out of it--one time, my Munchlax used it to get Judgment.
-Confuse Ray. Nothing is as annoying to opponents as a 100% accurate confusion move.
-Weather Ball. It can be a Normal, Fire, Ice, or Water attack, so it's like having four attacks in one!
-Toxic. I find it to be a wonderful move on a Pokemon with low offenses and high defenses, as it can take out a Pokemon by itself before too long.
-Will-O-Wisp. It just looks so cool... blue flames...
-Aura Sphere. A special Fighting attack with a power of 90 that never misses--w00t! I simply cannot keep a Lucario without it.
-Me First. Imagine using it on Cynthia's Garchomp when it uses Dragon Rush!
-Tri Attack. Being able to cause three status problems with the same attack is pretty awesome.
-Dream Eater. THE ultimate HP recovery move. Why in the world can't Hypno learn it by level-up??
-Dark Void. Putting two Pokemon to sleep at once is pretty awesome.
-Leech Seed. This is probably my favourite status problem, because it causes gradual damage and gradually recovers HP. I keep it on practically every Pokemon that can learn it.
-Perish Song. I love the idea behind it. Like Curse, I like to use this move on a trainer's last remaining Pokemon. I also like to use it in double battles.