I've finally reached that point where I need to sell off old gear to afford the new stuff (plus food, rent, etc...), so it looks like I'll be having a rotating collection from now on. On a practical level, I couldn't possibly use all the stuff I have now anyway, but that's not really the point.
The following are up for sale (PayPal only, CONUS preferred, extra shipping otherwise):
IEMs/Canalphones:
Altec Lansing iM616 - SOLD - Mint condition, with all accessories and the original packaging. I bought these to compare with my iM716 and wound up barely using them at all.
XtremeMac/Future Sonics FS1 - SOLD - Like-new condition, Black color, with all accessories and original packaging. This was purchased prior to the introduction of Future Sonics' new bi-flange tips and comes packaged with the original bullet-style silicones. Rarely used.
Philips HN060 - SOLD - Mint condition, with drawstring pouch and AAA battery. This is Philips' active noise-cancelling canalphone with built-in neckstrap. I bought it simply out of curiosity after reading some positive reviews here on head-fi, then moved on to other earphones, as is my way. 
Sennheiser CX300 - SOLD - Good condition, supplied with new small, medium, and large Sony EX71/90 tips. The earphones themselves are well-used but clean and well-taken-care-of. If you want to make sure you don't get one of the many fakes circulating out there, this is a sure bet.
V-MODA vibes - SOLD - Brand-new, Flashback Chrome color. I received this set recently as a warranty replacement but had already upgraded my earphone preferences by that point. I briefly opened the package to verify which generation they're from (2nd-gen, non-strain-relief) and to give them a quick listen before sealing them back up again.
Headphones:
Philips HP460 - SOLD - Mint condition, with original accessories. Great sound in a closed, portable solution. I actually prefer it to my K81DJ, but the fit is wrong for my freakishly-shaped noggin.
Audio Technica ATH-FC7 - SOLD - Fair condition, Metallic Gray color. I modded these by placing weatherstrip foam underneath the pads for comfort. In the process, I accidentally ripped a small part of the outer layer of pleather off the bottom edge of one of the pads. This exposed cloth area does not touch the ears when worn and does not affect the sonics or functionality of the headphones in any way. Otherwise, they were barely used.
Sony MDR-XD400 -
$40 shipped - Like-new condition, with supplied extension cord. The comfiness and wide soundstage make it a choice movie and gaming headphone.
Sennheiser PX200 - SOLD - Good condition, with plastic carrying case. The case is a bit scratched from regular use, but the headphones themselves are in flawless shape.
Sennheiser PX200 - SOLD - Good condition, with plastic carrying case. As above, the case is a bit scratched from regular use, but the headphones themselves are in flawless shape.
Philips HP170 -
$15 shipped - Excellent condition. Bought as a cheap, full-sized computer headphone. Used sparingly before upgrading.
Sennheiser HD205 - SOLD - Like-new condition, with original accessories (1/4-inch adapter and snazzy leatherette pouch). Impulsively bought and barely used.Earbuds:
I bought a bunch of these a while back because I wanted a collection of inexpensive, uber-portable headphones for my various portable devices (ignoring the fact that earbuds just don't work for my ears. As a result, none of them saw much use at all).
Sennheiser MX400 - SOLD - Mint condition, with winding case and extra pair of thicker RadioShack pads.
Sennheiser MX400 -
reduced price: $12 shipped - Mint condition, with winding case and extra pair of thicker RadioShack pads.
Sennheiser MX450 -
reduced price: $12 shipped - Mint condition, with winding case and extra pair of thicker RadioShack pads.
Sennheiser MX450 -
reduced price: $12 shipped - Mint condition, with winding case and extra pair of thicker RadioShack pads.
My ebay feedback can be found
here, and my head-fi feedback
here.
Thanks for looking, and feel free to PM me with offers as well.
-David