Im atually looking for new speakers now, and would like to know what others are using and if they are happy with their setup?
I've been using the classic 2 speaker setup for quite a while now in various forms. I don't use 5.1 because I don't believe the little satellite speakers carry enough clarity in the mid range frequencies and I don't use a sub woofer because I get enough bass out my speakers.
There are so many things to take in for account, like the size / shape of your room and what you're gonna be using them for.
Do you play games? If so then 5.1 is all of the awesome and you'll get lost in the atmospherics. If you just listen to music then either 2, or 2.1, but getting the sub would depend on the power of your main speakers and how much you want to annoy your neighbours!
I've got a pair of Tapco S5 Speakers...
With these you seriously don't need to have a subwoofer, I've got the bass being restricted and I only have the volume to about 25% of what they are capable of, but the sound quality is amazing and breathes new life into your music.
I'd say above all, if you like your music more than anything else, don't go for 5.1, satellite speakers don't have the capability of reproducing voice well enough unless you spend shed loads of cash on one of the top makes with chunky satellites and a larger center speaker, most 5.1 systems have just 5 tiny speakers that hardly weigh anything (usually the sign of a good speaker is its weight).
hope this helps