When friends ask for advice about which audio products they should buy, I generally try to convince them to think of the overall system, and give the following advice:
You can feel safe spending real money on transducers. They are the most important part of the signal chain, with the largest variance in quality between expensive and cheap. Also, they tend to be pretty timeless.
Digital to analog and analog to digital converters matter, but much less than you'd probably think. The difference between the adequate and the premium is quantitatively great and qualitatively small.
Cabling should be good enough to provide solid connections between pieces in the chain and that's it. Keep your cable runs as short as possible, use balanced connections when you can, and don't spend too much money here.
At the Marine Band, I was pretty spoiled with our budget for audio gear. I got to monitor my recordings on pairs of Bowers & Wilkins 804 and Lipinski L-707A speakers. We had several pairs of Sennheiser HD650 headphones lying around. Our microphone cabinet would make most audio engineers drool, with pairs of MKH800's, CO-100K's, Royer Ribbons, and more Schoeps than I could count. However, for D to A conversion, we used our DM2000 console instead of fancier options because it made our lives easier to have one fewer piece of gear and it was "good enough".
For my personal equipment, however, I have a much more limited budget. Hopefully spending some time describing what decisions I made and why I made them will help someone, without making me sound like an elitist audio snob.
In my living room, I have a 5.1 setup featuring B&W 600 level speakers (two DM603, two DM 602, and an LCR 6). There's also a JBL 12 inch powered sub back behind the TV, but I was too lazy to crawl back there and get the model number. (I don't recommend spending too much money on subwoofers. If you've bought good main speakers, you will have your crossovers set very low.) The B&W's are powered by a Harmon Kardon 2.1 amplifier. I bought all the speakers and the amp off Craigslist. I've found there are always rich guys looking to move up to something pricier or people getting rid of their big, heavy, boxy speakers in favor of something smaller. For me, big, heavy, and boxy are generally good things when it comes to speakers, at least in terms of what I care about, which is how good they sound compared to how much they cost. Also, since speakers really don't age, I see no reason to buy them new.
For switching between HDMI sources and converting the digital signals to analog, I have an Outlaw 975 surround processor, which I bought directly from them. You might say "But wait! you just said transducers are the most important thing! Why are you buying those off Craigslist, but you're paying retail for your pre/pro?" My answer is that although the fundamental technology used in D to A conversion may not have changed much in the past twenty years, the connections themselves have. Hopefully HDMI will be around for a while, but in case it isn't, I want to be able to swap out that component with minimal impact and leave the important stuff intact.
Connected to my iMac, I have a pair of Tannoy Reveal Active speakers I bought about fifteen years ago. I think I got them on eBay. When I got them, active nearfield monitors were just starting to become affordable. I haven't really found them to be lacking, but if I were to make that purchase today, I'd probably go with a pair of Neumann KH 120A's. Getting the signal from the Mac to the Tannoys is an RME Fireface 400. Choice of an audio interface is an area where factors other than audio fidelity come in to play. I probably wouldn't notice the difference in audio quality between an RME interface or something cheaper from a company like Presonus, unless I was comparing them directly. I always found the Presonus software to be buggy, however, and for the RME stuff to just work. A Benchmark DAC1 would probably get me a small fidelity improvement over the RME, but for the money, I know upgrading my speakers would yield more improvement. Also, RME interfaces allow me to use DigiCheck. I think the biggest thing holding me back from upgrading that eight year old iMac is that new Macs don't have firewire, so I'll have to resort to clumsy hacks or upgrade the Fireface as well.
I've rambled on for far too long now about gear, but hopefully this will help convince people that there exists a sensible center between Beats by Dre and audiophile excess. But if you enjoy either of those, that's cool too. It won't make me enjoy my setups any less.