In this economy?
The best time is when you have the credit/cash and want it, IMO. I think it's a pretty good time for consumers who do a little homework and don't get suckered by the latest Pavlovian conditioning that we call "advertising"
I think the old rules have been thrown out the window by the fact that business is suffering. Prices are continually (have been continually) coming down for products which have not been priced to sell to the unknowing.
I believe the key thing is to monitor a couple of key sellers (Newegg, TigerDirect) and realize that Walmart and other typical brick-mortar stalwarts...also offer lots of merchandise online at lower prices and availability which won't be found at the brick-and-mortars.
In my era...the best time to buy many things was just after the fiscal year for that enterprise ended. Reason was...that was the typical period where entities rid themselves of excess inventory which is no longer the featured item.
The more important decision...is not when, but where, IMO.