Pit is an obvious choice. Projectiles give Meta Knight problems. Thankfully, Pit is one of my mains. The shield could be used as an offensive weapon (this is a pro's tactic). Arrows are typical. I dont need to say anything else about this magnificient Angel ^^
Zelda causes trouble with Din's Fire. As we all know, Brawl's Din's fire has greater explosion range and is easier to control. Zelda's kill moves (The lightning kicks, U-Smash, F-Smash, U-Air and sometimes D-Smash) have chances of KOing Meta Knight before he hits the 100% line, especially U-air. Her teleportation, when used a lot (This is my strategy) can cause frustration for Meta Knight. The Projectile is the main reason.
Though I think Donkey Kong is 100% Meta Knight counter, he's still a decent counter. With all those KO moves, the Meta Knight player had better know how to avoid the moves before he gets to the 100% line, or lights out. DK's F-Smash and U-Smash are 2 dangerous attacks that can KO Meta fast.
Similar to DK's, Bowser is a Tank and it takes a while for Meta Knight to KO him. If Bowser's Power attacks connect, Meta Knight will be in trouble. Bowser is only effective in close-combat, and without Projectiles, Meta Knight must engage the Tank. Fire breath causes trouble when used correctly. In this matchup, skill can play a major factor in achieving victory. A pro Bowser could level even a pro Meta Knight if that Meta does not have much defensive skills.
I dont know why I'm mentioning a character I hate, but Pikachu... yea. His Thunder does good when Meta Knight is Gliding. I know this because my Pit suffered from some Pika Thunders by gliding (Even though i still say Pit is a counter to Pika). Pika's Projectile is also trouble.
A Link player that has mastered his projectiles can pose a threat to Meta Knight.
Marth outranges Meta Knight, but i dont want to talk about this guy, because I dont like him.
That's all I can give you. May it help you well.
This is the Admiral, Over and Out.