I signed up for the Best Buy newsletter, so I get the daily morning "Deal of the Day" emails. If's it's a video game, I normally just check the trade in value at Gamestop to see if the trade in value is worth a flip or not.
Gamers Club Unlocked at BB is much, much better than Power Up Pro at GS.
If you pre-order games for yourself or your children, they also always give out extra $10 rewards for pre-ordering and picking up select games which stacks on top of the 20% off you get.
http://www.bestbuy.com/site/clp/my-best-buy-get-10/pcmcat308100050002.c?id=pcmcat308100050002
Brand new game: $59.99
-20% off = $47.99
+$10 certificate
$37.99 for a game you'd pay $59.99 for anywhere else (as long as you pre-order).