If you've got a motherboard with a fantastic onboard card, then the $59-$79 group will be just above the onboard quality so the only reason you'd get one is to take the load off your CPU/RAM and/or to increase the connectivity if your onboard doesn't have the ports you want. If your motherboard has a generic made-in-China card, then that group will easily surpass the onboard. Generally speaking though, the top end sound cards are for audiophiles/music activity. "I want to hook my entire band into the computer at the same time" or "I want to listen to Bach and hear the violin squeak" are the usual groups who have the top end cards. Also the "I want to hear the guy crawling from the other side of the map in CoD" and "I want to play Serious Sam with on-the-fly encoding to 7.1" people.
Also depends on your speakers/headphones and sense of hearing. If you've spent $200 or more on a sound card but have a $30 set of speakers, then the quality increase in sound from the card is going to be negligible. On the other hand, if you've got hand made analogue speakers with a digital connection hooked up to a $15 sound card, then the card will be holding you back, and probably be just as good as the onboard. For the average person, a $70-$110 card is capable of dealing with everything you'll come across. If you're going to get some decent speakers/headphones though, it's worth investing in the better cards. Same as graphics cards and monitors.
I do have, IMO, an amazing set of 5.1 THX speakers that were made by Altec Lansing a few years ago, but to me sound just amazing. When I played Gothic, I could hear my enemies behind me, figure out which side behind me to turn around, and I've had several other people sit in this chair (I have the speakers optimized for this chair) and they've all gone away marvelling at the sound. The crispness, the detail, and fullness is very impressive. To me. But I am not an audiophile or whatever that term was cause I don't even know what that means. And I got that amazing sound for years out of a TurtleBeach/Santa Cruz card that wasn't all that expensive, and then my new rig had the onboard sound that actually sounded even better to me (it seemed to really handle the 5.1 channels better, if that makes sense).
Anyway, thanks again for the help. I'd really like to spend my dollars on performance and graphics and if I can save $100 on my sound card, I'd like to. But it's been so many years since I've purchased one that I just don't know whether or not the bargain ones are any good at all anymore and thus, that's why I asked.
HT|Omega "Striker", ASUS "Xonar", and M-Audio "Audiophile" cards are all in your price range. You can spend a lot more for high-end M-Audio, HT|Omega, or Auzentech gear. I hesitate to make specific recommendations, because perceived sound quality is so personal.
Avoid anything from Creative Labs and anything Fatal1ty whored his name for.