Just noticed this - the Xbox 360 version of Guitar Hero 5, game only, is down to $29.97 on Amazon.com. Update: Looks like the deal is now dead. Sorry.
All of this stuff below is now inoperable.
Of course, the offer to get Guitar Hero: Van Halen free with GH 5 has by now expired, but I don't think this is some discount off a drop in MSRP. Other retailers are still selling it for full price. But I don't know how long the deal is good for; it does not appear to be a lightning or Gold Box deal.
Again, this is for Guitar Hero 5 on Xbox 360 only and, just because someone will ask, it's the game only. That means no instruments.
Guitar Hero 5 is $30 on Amazon [Blast Magazine]