Cheap sound cards
The sound card provides the connection between your computer and speakers. As the old saying goes, if you get what you put in. You'll need a quality sound card if you want to realize the potential of your speakers and also to produce the highest quality sound possible.
BUDGET PC
For a budget PC, your money should go into other components rather than a separate sound card. Since integrated audio has become better these days, you can definitely use that.
If you want to buy a sound card as a separate part, (recommended if you are into making music and/or playing games) Creative Labs Sound Blaster Live! 5.1 is a good and cheap choice for a budget PC.
Creative
Labs Sound Blaster Live! 5.1 PCI Sound Card ( review
)
Creative Labs Sound Blaster Live! 5.1 PCI Sound Card is probably everything
you need for a good sound and it is the best deal right now. You won't need
this card if you have good onboard sound on your motherboard (unless you
play latest games). However, some of the older motherboards have bad quality
built in sound cards, which could give you somewhat scratchy sound. If you
have this problem, Creative Labs Sound Blaster Live! 5.1 is a good alternative.
BUSINESS PC
Any business PC should require no more than an onboard sound card. As your motherboard will probably provide an integrated sound carde (most of the new ones do) you won't need to worry about the sound card in this case. The only time you will want to get a sound card for a business PC is if your integrated sound is terrible and produces scratchy sound. However, this is very unlikely to happen with the new motherboards.
GAMING PC/HOME THEATER/MULTIMEDIA PC
If you want to have the ultimate gaming experience you definitely have to get Creative Labs Sound Blaster Audigy 2 ZS card ( review ). There is also a platinum version available but you will not need this one. Its around $80 more expensive and you probably won't use all the features if you just play games. Creative Labs Sound Blaster Audigy 2 ZS supports up to seven speakers plus a subwoofer.
I would also recommend Creative Labs Sound Blaster Audigy 2 ZS sound card for Home Theater and Multi media PC as it supports 24-bit audio and has DTS ES and Dolby Digital decoding. For the gamer, the audigy provides 7.1 speaker support and EAX 4.0.
If you are low on money you can also go with an older version of the Creative Labs Sound Blaster Audigy.