The Platinum 5.1 is a nice well rounded audio package. It is pretty much the swiss army knife of sound cards. MWAVE has the 5.1 platinum OEM (with livedriveIR and remote) for $137.00.
http://www.mwave.com/
The alternate to the Creative Labs card would be the Hercules Game Theater XP. It runs about the same price, but that's for the Retail boxed version! The OEM version retails for about $110-115. You can find the prices on pricewatch.com
There are differing opinions on these cards. Generally speaking, unless you're overtly nit-picky you'll probably not notice a difference in sound quality either way you go. If it comes down to a cost issue. You won't be sacrificing sonic quality if you get the cheaper of the two. That much I am sure of.
If you don't need a breakout box. The vanilla 5.1 creative card or the Turtle Beach Santa Cruz are both good options. Both cards fully support 5.1 speaker configurations, and both cards sound just as good as their more expensive brethren (the Turtle Beach Santa Cruz and Hercules GTXP share a common DSP).
As for speakers. I am partial to Midilands myself. They are affordable speakers and the quality is always top notch. The S4 7100 Plus matches up quite well with the 5.1 cards. For $200 you get a great package. If you want to save a little you can get the 7100 vanilla model. It runs for about $165, but you give up the flexibility of a nice Dolby Digital Decoder and Remote. In my opinion, it's worth the extra $35 to go with the upgrade.
If I were in your shoes I would probably get the Turtle Beach Santa Cruz and Midiland S4 7100 Plus.
Why? I actually regret purchasing the Creative Labs SBLive! Platinum. (The 5.1 wasn't out at the time.) I never really use the breakout box. Ok, maybe on rare occasions I use the headphone jack, but considering that I ended up just buying a headphone amplifier anyway the live drive turned out to be a total waste.) Plus, honestly I find it hard to justify spending >$100 on a sound card. It is much easier to justify spending the extra funds on a higher quality speaker system. (After all, that's ultimately where you'll notice the difference.) Not to mention that Creative is expecting to release a successor to the EMU10k1 DSP.
I hope I haven't muddled matters too much for you.
Just trying to throw out some opinions is all.
For some good reviews on all products mentioned go here...
http://www.3dsoundsurge.com/