Halo 4 is on sale for $39.99 on Amazon today, and comes with $10 in Amazon Instant Video credit. What was that you said? You have more money to spend? Well you're in luck, because a PC download of Hitman: Absolution is on sale for $29.99 on Amazon as well, with Xbox 360 and PS3 versions at $39.99.
Halo 4's Crimson Map Pack arrives December 10. For those without a calendar, that's tomorrow, which makes today's sale rather convenient.
http://www.amazon.com/exec/obidos/ASIN/B0050SYX8W/
http://www.amazon.com/exec/obidos/ASIN/B007VFHIHA/