Well, after much consideration, you could probably get into a nice Reciever for your budget amount. At which time, maybe hit the garage sales for speakers to 'get you by' until you can make another plunge dropping another 700+ for speakers. The only reason why I say this is, is that you obviously want a good/great/best system. One question for you though, what is an example of the best system you've heard? I assume that's your reference point of what a good system sounds like. Anyhow, we should be able to find a desent receiver for $550-$700. As GG said, you don't need to buy it all in one go.
Another consideration, when picking out speakers....you said that speakers didn't matter, home, car, whatever. Well there is some considerations with the speakers Ohm or resistance capacity. Most consumer Home audio systems are based on 8 ohm loads. High End, audiophile or Pro Consumer Home audio is usually based on 16 ohm loads. Car audio runs at 4 ohm loads and below. So...., what I'm saying is, make sure if your going to hookup Car speakers to a home theatre amp, make sure the ohm loads are consistant with what the amp can handle. Don't hookup a 4ohm speaker to a 8ohm load amp.
Also, on the topic of Ohms, the higher the number, the greater the resistance which means you need more power to create the same db, however, at higher ohm loads, your power and signal to noise level with less, providing you with much cleaner power and sound.