If you haven't picked up the Burning Crusade yet, congratulations: you've saved yourself 3 bucks. Techbargains points out that Newegg is now selling the expansion for $36.90 with free 3-day shipping, which is the cheapest we've seen it yet.
And if you don't have the new expansion yet, it's pretty clear by now that it's worth it at under $40. Originally, I was thinking that if you haven't got a 60 yet, it might not be necessary, but considering all the great new content that showed up in the starting areas, anyone interested in rolling a new character would definitely get their money's worth.
Of course, if you're willing to hunt a little bit, there are even better deals to find. The Collector's Edition, sold out in most places, is still floating around on eBay, some for even cheaper than this Newegg deal. Of course, that brings all the risks associated with normal eBay deals, but no matter how you find it, there's almost no reason not to pick up the expansion and take on the Burning Crusade.