Auzentech <> ASUS > Realtek (latest onboard chips) > Creative
With EAX all but dead, it comes down to quality of output and features, where Creative is lacking to say the least...Auzentechs newer models are based on the Creative X-fi chipset, but using much higher quality parts, making the chipset much better. ASUS uses the C-media chipset, which is just as good, but lacks authentic EAX support (though they do emulate EAX 5).
In the sub-$100 range, ASUS and HT Omega (who uses the same C-Media chipset) are king; you have the low end ASUS Xonar DS, and the mid-range ASUS Xonar D1/DX and HT Omega Striker.
Moving up a bit, you get to the price range of the ASUS Xonar D2/D2X, and a bit higher, the Auzentech Prelude, which are the most "complete" cards feature wise.
At the top of the line, you have the ASUS Essence ST/STX, HT Omega Claro, and Auzentech Forte, their main add on being a powered headphone amp.
For the HTPC crowd, you have the ASUS HDAV1.3 Delux and Auzentech Home Theatre HD.
For under $100, I recommend the HT Omega Striker [unless you want the emulated EAX 5.0 ASUS offers], mainly due to support for both Dolbly Digital Live and DTS Connect [The DS offers DTS-C, and the D1/DX offers DDL]. Above that, the D2/D2X and Prelude offer the best blend of quality, features, and price. Still, the powered headphone amp of the ST/STX, Claro, and Forte is attractive to some buyers...
With better cards avaliable at a lower price, there is no reason to go with Creative anymore.