If the Air Cushions are just slightly better than the marshmallows, then I'll have to pass on them. The marshmallows just did not impress me at all.
The Lenntek sonix look very promising. I like the fact that the buds are metal and the cord is made out of nylon, so they're fairly durable. The reviews are great about them. Have a lot of bass, which is good. They're 10 dollars cheaper than my budget too. The only gripes I have with them is that they don't come with a carrying case, and they're red. I can just use an old tin as a case, but I don't like red... Oh well. I might just have to go with it anyways.
I think that I'm done looking at the NE-7Ms, RE2s, and i590s. They're just too expensive for me.
If the only 2 options I have are skullcandy's or marshmallows, then I'd go with the SkullCandys again. They sound good, but I'm fed up with having to replace them within a few months of buying them.
A good seal is quite important, so I think the Ai-M9's are out.
So that leaves the Lenntek Sonix and the PL21. I'm heavily leaning towards the Lennteks right now, but is there anything that the PL21s have that would change that?
Edit: I want to order my new headphones within 3 hours from now. Being headphone-less is terrible, even if you're not an audiophile...