First, free shipping, they all do it. But at wildly different levels ($100 AutoZone, $75 O'Reillys, PepBoys, $50 Advance).
But the king of 'sale' is Advance... every time I go online they have at LEAST 15% off $50 PLUS a coupon for $25 off your next $50 online order. None of the other online parts places had this.
So, I order a distributor/cap/plugs for the G506, roughly $95 in parts (includes shipping to my home, taxes, less the 15% off).
Today I order a new serpentine belt, tension pulley and 1 gallon of car wash (had to hit the $50 mark for the $25 off to take effect).
So the total came out to:
Product Subtotal: $55.27
Discounts: -$25.00
Shipping Charges: $0.00
Tax: $1.82
Total: $32.09
Some quick math: $32/$55 = 42% off!
I also got a huge deal on tires.. although this time it was PepBoys (Buy 3, get 1 Free, plus 15% off if ordered online).
30x9.5x15 tires were $136 each (ignoring the fees/taxes etc) $136x4=$544 vs $136x3=$408 $408/$544=25% off BUT that didn't include the 15% discount for ordering/schedualing installation online... $408-15% = $346 for FOUR TIRES, INSTALLED (plus the tax, disposal fees etc) I was out the door on 4 new tires for just at $400.
Go ahead and price 30x9.5x15s.... see if you can find them for $100 installed

Bottom line... if you are not taking advantage of these online offers you are leaving some BIG MONEY on the table. Just these two examples saved me $200.