Cart before the horse or horse before the cart?

So, I'm finally building my first home theater and just purchased the TV, (LG PK950)so far very happy with my purchase.

My question is, if you were going to be starting with nothing, would you buy your receiver first based on your needs and then the speakers, or would you buy the speakers first and buy your receiver that best compliments your speakers? I've read so much about different receivers better suited for different speakers.

I'm undecided on speakers at this point, but I know I'm going to be buying used, betting I can get better quality for my money.

Paradigm Studio 20's or 40's
Usher S-520
Energy RC10
B&W 6 series, etc.

Reciever: Not sure at this point, Onkyo, NAD, Marantz, Denon...

Honestly, there are so many opinions and when I think I've got it figured out something else comes up...need a little help please.

speakers $500-$600 (used bookshelves)
receiver $700 max

For now, just the two bookshelves and receiver.

System dedicated to mostly HT and some music, IPOD and vinyl, punk and garage.

What do I purchase first? Thanks everyone.
What do you currently own?

Personally, I would suggest getting the least expensive receiver that you can that includes pre-out for all channels. This will give you the option to combine it with a dedicated 2 channel amplifier in the future for the best music listening. I think "requirement" might put you in the $800 range for a new item. Speakers don't get dated when it comes to technology, but receivers can. You want one that will handle all of the lossless blu-ray audio formats and HDMI 1.4 that will do 3D TV just to be current with technology.

You'll want to plan for a subwoofer to make a 2.1 home theater for the best sound.
Something similar to a Pioneer VSX-1120-K would be a great unit as it's very current with the latest technology.
I don't currently own a receiver or speakers...recently moved to another city and now am starting from scratch. I've been looking at the Onkyo line of receivers, 608, 707, and 806...haven't thought of pioneer I'll have to check them out, Thank you.

So, it sounds to me like I should purchase the receiver first based on my current and future needs?
Speakers first. Because they might be 4 ohms, and then you need a receiver that is good into 4 ohms.
I got a set of Canton new 300's (4) and 360's (3) at 30% of retail at a blowout/closeout dealer sale. (still in the boxes and yes that is 30% OF retail, not 30% off)
I got a nice demo Denon 4806 at the same sale, half off.
I am certain I will never bother to upgrade the speakers, I like them very much.
Speakers first as the amp needs to match the speaker.
For the speakers, I've pretty much narrowed down my search to Paradigm Studio 20's or 40's, whichever I can find for the best deal on used, PSB GB1, and Totem Rainmaker.

Any recommendations for a receiver? I guess I've been leaning towards the Onkyo line (608, 707, 806) because of all the features and I can get at a very good price from a certain online dealer..(don't know if we can name dealers on this site).

Mceljo recommended the Pioneer VSX 1120 K and that seems like a nice choice...any others I should look into?
I know I should audition all of this, but the closest dealer to me is 2 hours away and they only have the paradigm.
If you're not wanting the option of pre-outs to step in the future to a 2 channel amplifier then you can drop several levels down in that same line and get a VSX 820 that should have plenty of features for less money. A friend of mine recently purchased this model for his 2nd system. He uses a Pioneer Elite model in his home theater room and used the 820 to run the rest of the speakers in his house.

Onkyo and Denon are also great options, I prefer Onkyo over Denon simply because they are a bit more user friendly with individual buttons on the front rather than a spin selector knob.

In my opinion, the two most limiting features in a receiver in the long run is not having pre-outs or 4 ohm capability. Both of these features add to the cost so you need to figure out how much it matters to you.

I also don't think that in the price range you're looking at that matching speaker and receivers is as critical as it obviously is in the higher end gear. I don't think the difference between a Marantz, Denon, Onkyo or Pioneer will make a significant difference with any speakers you'll be considering.
Onkyo TX-NR808 would be a great option from the online retailer that you speak of. A co-worker of mine just purchased one and seems very happy with it.

It is rated for 4 ohms and has pre-outs. The current price is right in your range.
Thanks for your responce Mceljo. I agree that the speakers and receivers I speak of within my budget probably don't apply as much as you say with the high end equipment, but being new to all of this, I really needed some confirmation in what I thought to be true.

Thanks again, I think I'll take your advice and find the right Onkyo for my needs. The TX-NR808 has the 3-D ready feature which I'm not interested in, but I do like the option of pre-outs and rated for 4 ohms. Does the TX-NR808 have a little brother which is not 3-D ready?
As far as I know, the 3D feature is just the latest HDMI connection. I don't think there are any specific features built into the receiver itself.

The TX-NR708 has all the same features with less rated power per channel but still maintains pre-outs and 4 ohm performance I believe.

Unless the price difference is significant for you, I'd get the 808.
To answer your question, the previous year TX-NR807 wouldn't have 3D capability, but the majority of current models will have the latest in HDMI technology and that means 3D capability.

Another co-worked just purchased the 2nd to the lower Pioneer in the line I previously recommended to you and it was 3D capable for under $300. I believe the most entry level Pioneer is 3D capable.

Personally, I like the idea of being as current as possible with receivers as you never know where technology will go next.
Thanks again, I appreciate all the help. Looks like I've got a decision to make, but you've made it much easier.
A little more information to help you in your decision.

My previous receiver was an Onkyo TX-SR606 that was rated for 90 wpc and continuous 6 ohms performance. My new receiver is an Integra 50.1 that is rated for 135 wpc and continuous 4 ohm performance. The improvement in sound quality was dramatic. I don't know how much to attribute to Integra vs. Onkyo, 135 vs 90 wpc or 6 vs 4 ohms, but the spec differences are similar between the 708 and 808 that you are comparing. The difference is that both are 4 ohm receivers.
Unless your HT room is 10'x10' or smaller I'd return the 50" plasma and pony up the extra $300 for the 60" and deal with the audio after the holidays. Everyone will give you krap about, "is your TV big enough". The second you turn it on all you'll hear is wow.

Does LG stand for Lucky Goldstar?