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I've got a set of cheap $15 Sony behind the head sports headphones from walmart. They are the right angle plug and work perfectly with the bumper.
 
I got the Ultimate Ears 700s a couple of weeks ago, and they work perfectly with the bumper.

The only downside is that they don't have controls or a mic on the cord, so you lose the convenience of the original Apple earbuds, but the vastly improved SQ makes up for it.

I have been looking around at various adapters which place the controls and mic inline, but haven't found one yet that looks appealing. They all seem to add an exra 2 feet to the cord, and also look incredibly cheap/crappy.

I did see someone who recommended grafting higher quality earbuds onto the original apple cord, which would be a simple task, but I am hesitant to hack up my $200 earbuds(although I got them for $70, missed out on the freebies by a few minutes)
 
Some of the regional Sennheiser sites list a PX-100-IIi (try Googling for that!) which is the same set of headphones with a proper volume-and-clicker remote and mic. No idea about a release date or price but presumably they're not far away.

http://www.sennheiser.com/sennheiser/home_en.nsf/root/private_headsets_mobile_music_504162

Nice! Those are perfect—even the plug looks extra-slim for use with cases, judging by the photo. And the volume controls have been added, just as I was hoping for. Those will be my next headphones... once I find a sale price :) Thanks for the heads-up.

P.S. Here’s a general link I found about 8 Sennheiser models that have iPhone remote controls and mic:
http://www.senncom.com/comm/home_en.nsf/root/press_releases_travel_line

I’m assuming those all share the slim plug too.
 
I would've thought that any headphones which claim to be iPhone compatible (i.e. fix in the original iPhone's recessed jack) would work with the bumper, by the way.

I thought so too! Unfortunately earphonesolutions.com doesn't. The Shure SE215 doesn't work with the Bumper case. They suggested altering the Bumper case or returning it (less a $15 restocking fee, shipping back AND reshipping fees) I suggest before buying any headphones checking the reseller's return policy beforehand if you are using the bumper (or any other) case for the iphone
 
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