I've never liked remotes on the cable, they get in the way and weigh the cable down when you're wearing the headset. For that reason I got the Logitech G35 which has a roller and some buttons on the earcup, and I can really recommend them. The Corsair Vengeance 1500 also delivers excellent sound. Haven't tried the Megalodon but have owned the cheaper Carcharias and was not very impressed - sound was very average and felt a bit flimsy.
Well they're a bit cheaper than the Megalodon but they're the highest end headsets from Logitech and Corsair.
Well I've had mine for about 3 years and it's never had a problem, but I treat all my gadgets carefully. In terms of general build quality I'd definitely say Logitech is superior to Razer, although Razer do seem to be improving. Logitech's customer service and RMA process is second to none though.
I can recommend Steelseries, got a Siberia V2 and had the original Siberia before, good sound and fits extremely well.
Can't really give any more personal recommendations as the G35 and Vengeance 1500 are the only gaming headsets I've tried. They are both USB with built in sound cards so you don't need to buy a dedicated sound card and you can switch between the headset and speakers on a software level (rather than plugging and unplugging cables for analog headsets). I think the Corsair is slightly more comfortable and is better suited towards music as the bass and mid ranges are better. The Logitech has excellent positional audio though, and eventually I went for them because of the buttons and volume roller on the side which are extremely useful.
No idea about that I'm afraid