1) Sennheiser HD650 (w/Zu and Headphile XLR) - For as long as I've been in this hobby, I've been a Senn guy. The sound is just so warm, full and smooth to me.
2) Sony MDR-SA5000 - Wow, the clarity of the sound is quite eye opening. The highest compliment? Made me rethink whether I was indeed a Senn guy.
3) Grado SR325i - There are some music and some amps that I just don't like with this, but otherwise it's an incredibly fun, forward headphone. The sound is bright and punchy without being sibilant.
4) Sony MDR-CD3000 - I don't listen to this nearly enough and I suspect that if I did, it might creep up to #3. Haven't place my finger on how to describe the sound. Everyone says they're bright and I agree, but they also have a liquidity to the sound.
5) Beyerdynamic DT531 - The "groovalizers" is an appropriate name. Very smooth, warm sound with good bass. Not quite as detailed as the cans above.
6-tie) Beyerdynamic DT250-250 - Currently my closed cans of choice. The sound is dark and easy to listen to.
6-tie) Audio Technica ATH-A900 - Formerly my closed cans of choice. They sound a little honky in comparison to the CD3k and DT250 but they're solid all-around performers and are easy to drive.
8) Sennheiser HD25-1 - Very light which makes them ideal for portable use. I haven't tried the cable upgrade yet but I plan to. The sound is punchy and crisp.
9) KSC-35 - While they may be #9 on my list, I strongly believe they represent the best value on this list. I'm continually amazed by the sound out of these cheap cans. Some say the bass is sloppy but I think it's perfect.
10) Sony MDR-V6 - One of my first high quality headphones. They are a little bright and sibilant for extended use but they do have a wow factor for those new to the hobby
11) Shure e3c - When I upgraded from the e2c, it was like a veil was lifted over the sound. You do lose some bass, but it's actually not bad at all with an amp.
12) Sennheiser MX400 - Ridiculously good sound for $15. Nuff said.