Surprise, surprise...the Best Buy kid tells you the Denon sucks but the Yammie is great. Wonder which brand
they carry?
Rule #1: practically everyone at BB is an idiot. Oh, sure, by dumb luck you might talk to a kid who happens to know his stuff, but that's the exception that proves the rule. At any rate, the Denon 3805 is a stupendously good receiver. I believe you can read a review of it here at AH (I think it was posted already- if not, there's plenty o' rave reviews of it in many respectible mags, online and off).
The $1k receiver price point is hotly contested, and all the big makers try to stay competitive. Denon is always a top contender, but in truth all the good companies make a pretty good HT receiver for that money. Go with the one who's remote you like the best. That will be your main interaction with the unit, so be sure you're comfortable with it. That's the only area the 3805 has been criticized, BTW. Note: depending upon your needs, you can get 95% of the technology of the Denon AVR-3805 for a few hundred less in the AVR-2805. It will have a little less power and a couple less inputs, but should still be "more receiver" than you'll need.
It's hard to give advice on speakers. Opinions vary wildly, and it depends upon your personal preference and your listening habits. Will it be for music, or mostly HT? What type of music do you listen to? How loud do you play your movies & music? How many will typically watch a film at one time?
My own feeling is that Def Tech speakers aren't a great value for the money- but I'm sure that there're half a dozen guys here who'd disagree with me. That's something you'll have to find out by listening. Top sound-per-dollar companies: Athena, Axiom, Epos, Monitor Audio, Paradigm, PSB, nOrh & Energy, just to name a few. There are others, but the ones listed here make very nice speakers for not a lot of cash.
You're off to a great start with the TV & DVD player. You probably greatly overspent on the cables, but you live and learn.
A good sub is a near necessity for HT, and a boon with music, too. Hsu Research, Adire, SVS, Outlaw & Axiom all make some good subs that won't break the bank.
One possible rig:
Receiver: Denon AVR-2805. $900 MSRP, about $825 "street" from auth dealer.
Speakers:
Mains: Monitor Audio Bronze B4. 2-way towers with good bass & dynamics, excellent sound. Synergistic with Denon, IMO. About $425/pr.
Center: Monitor Audio Bronze Center. 2 & 1/2 way speaker minimizes lobing d/t horizontal layout. Dynamic with good bass. Approx $200.
Surrounds: Monitor Audio BFX. Can be wall mounted and configured as bipole or dipole as you desire. Bass response is consistent in either config, unlike many dipoles. Available in white, too, to match walls. Approx $300/pr.
Sub:
Hsu Research STF-2. 10" powered sub, 200 W amp. Single tuning frequency with superb extension and great output. Very tight and musical, yet capable of room shaking HT bass. Factory direct from HSU for $399 + $25 shipping.
This would be a superb system for both music and HT. The MA speakers are very synergistic with the Denon gear and are fantastic for the money. They're very detailed with a tremendous midrange. The Hsu sub will improve the dynamics and extend the bass solidly down to the 25 hz range. It would satisfy many people for many years. Bear in mind, this is a low/mid price rig, depending upon your point of view. MA makes 2 lines above the entry level Bronze's, and each step up gives you better sound. But the Bronze's are a great blend of clarity and power at a very low price. The total damage would be about $2100, give or take, and you'd be hard pressed to come up with a better all-around system for the money.
But it's only one option. This is the best time in history to get into HT, and good sound has never been so cheap. This forum is a great place to start, but ultimately you'll have to listen for yourself to see what floats your boat.