Just seen this on Major Nelson, looks like xbox.com is having a ridiculous sale on Games On Demand starting from the 19th June.
This is the entire list that was listed aimed at USA only but the deal applies if that game is available in our region (i.e; UK) - $4.99 is basically 400 points, so all these games will be 400 points each on the 19th June for a full week:
I admit some of the games are rather old, but not bad for 400 points for an easy 1000 achievement points.
Blazing Angels: Squadrons of WW II
Bomberman Act: Zero
Cloudy With a Chance of Meatballs
Meet the Robinsons
Perfect Dark Zero
Prince of Persia
Rockstar Table Tennis
SEGA Superstars Tennis
Tom Clancy’s Ghost Recon Advanced Warfighter
Virtua Tennis 2009
Viva Pinata Party Animals
Just had a look at what is available in the UK: The following games aren't available:
Bomberman Act Zero
Meet The Robinsons
"Update: I was just told that sale has been extended a week until Tuesday, July 2nd"