I am no sound card expert, but I do have quite a bit of experience when it comes to audio equipment (I do recording, editing, mixing). I've gone through a number of sound cards, from the low-end $25 stuff to the STX/Ti HD to Professional-Level audio cards. However, I actually use my PC primarily for gaming, "regular usage" (internet etc), watching video, and of course listening to music.
I have a Rampage IV Extreme (3930K) and thus the Realtek ALC898 CODEC for my onboard audio, which is currently the "top-dog" outside of the few boards that have added Discrete Audio Processors into the MB itself (the Creative "SoundCore3D").
I would recommend, in order of personal preference (for gaming):
1) Creative X-Fi Titanium HD - excellent gaming performance without compromising much when it comes to music or movies; SNR is very high, and despite their lacking any decent headphone amplifier they still power my Grado PS1000's, RS1i's, RS2i's, SR325's, Audio Technica ATH-AD900's, and so forth, and I have never heard the card cause any of the sets of 'cans to distort (even at un-wearable volume levels). Audio positioning is excellent, whether with headphones or with a 5.1ch speaker setup; I really think that this is the best "all-around" sound card you can get...
2) Asus Xonar Essence STX - pretty well tied with the Ti HD, the difference being that the STX is better with music/movies but somewhat inferior in games (not to say it's "bad" in games, not at all!). This is a very "musical" card, and it simply feels "more at home" playing a Song in 192Khz/48bit Loss-less format than it does the compressed and occasionally-overbearing "spikes" that make up much of video game audio tracks. However, we're talking about very small differences, ones that the majority of people wouldn't even notice... This is, undoubtedly, an EXCELLENT CARD!
3) Asus Xonar DX - best bang-for-the-buck, especially if you use headphones as it seems to give about 90-95% of the STX's/Ti HD's quality in 2-Channel Stereo Headphones for less than half the cost, so long as you're headphones are no more than around $150 or so (just a general price range where I've noticed the quality of headphones takes a sharper upward curve; you get the same thing around ~$50, ~$90, $225, $375, and $600). I think this card sounds phenomenal on my ATH-AD700's, SR225's, SR80i's, and so forth, but I do notice that it doesn't seem to quite be able to keep up with my PS-1000's, RS1i's/RS2i's, ATH-A900X's, D9000's, etc. With this card, I would HIGHLY recommend getting a pair of the Audio Technica ATH-AD700's, as it seems to really like the open-air (Dynamic) headphones over the closed-ear type.
4) Creative Z/Zx/ZxR - have only spent limited time with the Z and Zx, but they seem to be capable cards (I am looking forward to seeing what the ZxR brings...), but for the extra $10-20 the Zx is the better choice (convenience features, mostly, but seriously worth it). The gaming and film performance is excellent, while the music performance is "above average", IMHO, which makes them essentially a more "gaming-oriented Titanium HD"; this is not a bad thing, but if you already own a decent sound card, the new "Z's" will likely be more of a side-grade than an upgrade. I have only gotten to use the cards with ~10 of my sets of headphones and only a few of my studio monitors, so I am reserving full judgement until I am able to do so. Still, even with some expensive audio monitoring equipment, the output over my Behringer TRUTH B3031A's (bi-amped using 12GA six-layer-shielded silver wire with 24K Gold-Plated pure-Copper-Core banana connectors) was absolutely the same as it is with the Titanium HD, with all equalizer settings disabled. In games, the Zx seems to offer SLIGHTLY better positioning, but in music and movies it seems to fall a bit "flat" (so-to-speak) in the mid range and has trouble separating some highs. When hooked up to my KRK Expose E8B Studio Monitors (same wires/connection), which are a significant step-up from the already amazing Behringer monitors, I noticed a slight "humm + buzz" sound from the speaker when the computer was on but there was zero audio coming out. I plugged the speakers into the ALC898 output and the buzzing was gone, and I run everything on isolated circuits with a line conditioner for the audio equipment and a 2500VA UPS for the computer, so there is no ground looping. Swapping out cards, and I couldn't hear the same sound on any of the other ones listed above. No bulging caps, no solder "trickle-over", no crossed wiring...in fact I could find absolutely NOTHING that would explain the sound.
I DO look forward to testing the ZxR with it's dual quad-core sound processors courtesy of the daughter-board.
The above are just my impressions, using a variety of equipment. I hope they help you in making your decision.
*For what it's worth, the ALC898 sounds decent so long as you are using cheap speakers or headphones, and if you never have used a GOOD audio card before it can sound pretty good up through the $150-200 range, but beyond that and it WILL start to show its weaknesses....