I personally do not believe that headsets are any good currently. A few of them are decent, but good...bah! I was facing the same dillema as you at one point. I started doing some research and talking to true audiophiles. What I found out was amazing!
Really it boils down to this. To get the best sound, you need good headphones. Headsets are a convenience, but not all that good. You can purchase a really good set of headphones and then by a clip on mic (such as the Zalman clip on mic).
After making the decision to go with headphones over headsets, I focused my research there. I narrowed it down to four (4) pairs of headphones (and this was last February mind you):
Seinheisser HD580
Seinheisser HD595
Beyerdynamics DT770 Pro/80
Audio Technica ATH-A900
After much discussion with the crazy audiophiles over at head-fi.org I narrowed it down even more and decided that the ATH-A900 and the DT770 Pro/80 were the best two for a mix of gaming and entertainment. The Sennheiser's are awesome in their own right, but I decided against them after about 2 weeks worth of research and discussion.
All of this was being done with 3 of my clanmates as well (we play FPS' mainly). Two of us went and bought the DT770 Pro/80's and the other two bought the ATH-A900's. All 4 of us are thrilled! I mean seriously...until you have a true set of headphones...you don't really know what sound is! I bought the simple $6.00 clip on Zalman mic which works flawlessly and now my setup is complete...for the most part (see below).
Now, keep in mind, this is said assuming that you already have an X-Fi soundcard or equivalent from another brand. One of the things that I am considering adding to my setup is a headphone amp, the G7. That will make the sound even more dynamic. Is it needed or necessary? No, but I'm looking to take my headphones to the next level.
I have used many headsets personally and have tried many more that friends have owned, but none can even compare to the sound quality of a true pair of headphones such as the ones referenced above. Granted, the cost goes up. My DT-770's go from $240+ at retail, but I went on e-bay and made an offer on a pair from a music retailer and was able to get them for $140.00 "brand new." Add on the $6.00 mic and it all came out to about $160.00 with shipping and tax.
Maybe this isn't for you, but it's just another alternative to consider if you want that TRUE sound that you appear to be looking for as I was once. I strongly recommend you talk to some cats over at Head-Fi.org though. These guys know sound and many are gamers as well so they are unbelieveable resources in this area.