I used to work at a Rex TV store (about 260 stores in chain) We often had coupon sales that amounted to about 10 % off at any given time. Sometimes it was coupon plus any sale price as well.
Friday morning after thanksgiving we would have double coupons + any sale prices as well. This could sometimes mean a $5000.00 TV for $4000.00. Smaller chain stores can give good deals sometimes.
a couple hints to negotiating.
Be nice. don't be an ***. Why should I give a good deal to a mean person. You would be surprised how many people forget this. 
Ask for a deal. You would be surprised how many people forget this.
Don't be afraid to ask about price guarantees. Buy it today if you can get next weeks sale price if it's better than todays price. I've seen plenty of people wait for a better price this time of year only to come back and find the item they want sold out. If it's in the box now and you want it, get it. Use a credit card for quicker price adjustments
Ask if the salesman works on commission. These folks want your business and will work to make you happy. I know because I worked straight commission for 5 years. BTW... Refer back to "BE NICE".
Know what you want and how to describe it. Don't waste a sale persons time... especially during the holiday season. I had a lady get mad at me one time, yelling at me "listen, I've been shopping since 6 this morning"... I didn't tell her that I had been working 16 hour days for the past 3 weeks and would continue to until the day after christmas. This time of year Time really is Money.
If you like the sales person and they have worked hard to help you, to educate you to the products features, to show you different models... then buy it from them. If the price difference is 50 or 100 bucks from one store to another then give the friendly salesman a chance to match it or offer an extra to make up the difference. Heck, if they can give you better service then spend the extra bucks. Look at how many "I hate best buy" rants are on google.
Unless it's a privately owned store - don't ask what price you can get for cash. The computer cash register doesn't differentiate from cash. We always got a chuckle from these pony traders.
Knowing what the product is, what it's worth and what you want is the key to any good deal. Asking for the deal and being nice while doing it is the other part.
I know there are a couple other people reading these forums that sell electronics. Any comments or disagreements?
grim