Also forgot about the HDR-R10 (Japan version of the DX100, not sure if it's much different besides more support for formats).
Also the Altmann Tera Player is great. I own one myself. Highly recommended if you think it could work for you. It's definitely not for everyone.
I have heard the DX100, it's nice. Very impressive, just a bit outdated with the unsupported Android OS (2.3.1, whereas 2.3.3 would be supported).
Colorfly C3 and Colorfly C4 are two options worth considering. Good reviews on both, C3 is much smaller though (so I've heard). Havent heard either one, but worth noting.
As far as high-end audio players go, it gets a bit hard to find out as most wont have all the different options to compare. Walkman DAP's seem to have lots of followers. I would suggest the iMod option if you go for an iPod Video (5.5Gen). That's how you'd get the most out of it.
I think DAP's are more than just about audio quality. You're on Head-Fi, you care about your music, but also, you make investments so that you can enjoy your audio to the fullest. Picking the right device is important because you're likely hoping to only buy one of them. Think about your usage and what exactly you want. Do your research and you'll be happy you did. Good luck with your search for an audio player to fit your needs.
EDIT: I think it's necessary to share some experience with you. Through my time as a member, I have used the Sansa Clip Zip, iPod Classic (7th gen), iPod Video 5.5 Gen and Tera Player as my primary DAP's. I used the iPod's with an external portable amp, which honestly can make a world of difference sometimes. I had a Pico Slim that made the Trebles from both iPod's sound luscious and magnificent. The Sansa Clip Zip is by far no slouch. It is a sleeper. It looks like a nothing. It costs pretty much nothing, but man if you dont need much to it, it is a great sounding little device. Definitely cant go wrong at it's price.
The Tera Player is a highly expensive device, but I love mine. I didn't pay full price, got it from a member selling it to make room for their home rig. IT's also very small and great sounding. I think the beauty of the Tera Player is in it's jitter free implementation. It is noiseless. Extremely black background and even sitting for hours next to my and others cell phones, I experience no interference like when I used my iPod with an amp. It doesnt have a ridiculous amount of power for headphones though, but if its a portable headphone, it'll be driven well or decently by the Tera.
Something has gotta be said about the iPod being around for so long and bringing about a lot of change in how the world works. It definitely is a solid device and if you take care of it, you can use it for years still, and enjoy it as well. The iPod is honestly best with the iMod modification done to it and a portable amp being used. This will get you the most out of the device, and also allow those less knowledgeable to navigate and listen to your music.
Just remembered, the Teclast T51 (AKA Nationite S:flo2) is also highly regarded, though known to have a bad GUI, which is also a complaint about the DX100.
EDIT 2: Forgot to mention the Hisoundaudio Studio V (especially their third anniversary edition) is another high end audio player. I assume you also know about the HM-901 which not much has really been shared even though some people should already have the device. Again, I preach research, questioning, and even demoing devices till you are 100% sur of what you pick if you are not seeing this as a stepping stone, but rather an ultimate setup.
Edited by kenman345 - 9/6/12 at 10:12pm