Beware that this thread could quickly deteriorate into a religious war over the best audio equipment. What's fundamentally important is that you like the way what you buy sounds. No matter what you get, someone else will claim it sucks.
Given that your mileage may vary, here is my opinion:
I would recommend a receiver/speaker combo over a 5.1 all-in-one speaker setup unless you simply don't have room for the receiver. The receiver/speaker combo is much more upgradeable/expandable.
I just bought, for $300, a
Denon AVR1604. There are other similarly priced models out there, one in particular is the
Onkyo TX-SR502, which costs the same and which I basically didn't get as the result of a coin flip - they are very, very similar, and the Denon just happened to be available at a store 10 minutes away, whereas the Onkyo was out of stock at another store 12 minutes away. If you spend more, you'll get more. If you spend less, you'll get less. For me, since I was replacing a very nice receiver that my 3 1/2 year old destroyed with juice, I bought something reasonably decent. I am very, very happy with the Denon. I couldn't justify spending a ton of money, nor did I want very low-end stuff. Having listened to both, the Denon and Onkyo are both very good mid-range systems and would satisfy 95% of users. You could be happy for less, but you won't find much with optical in for under $200. Please try to find something you can see, touch, and
hear before you buy it - internet pictures only get you so far.
As far as speakers: I got a set of Polk R20's (now discontinued) when they were on sale at Circuit City, and a
Cambridge SoundWorks Classic Series CenterStage Center Speaker . I also have a
Polk PSW1200 Subwoofer that is massive overkill for what I need - but I have it, so I'm going to use it.
However, I believe that you can "go low" on the speakers and still be better off than most all-in-one speaker systems. If you need to save money, buy a speaker package. I've seen very nice ones as low as $150 on clearance. Here's
one I've heard for $150. Yes, it isn't phenomenal. But, for $150, it's very very nice. Add that to the Denon or something similar, and you've got a very nice audio setup with great expandability for under $500.
If that's too much, I've seen home theater setups for under $250 with optical input.
Best of luck with your decision, however you decide to go!