Square Enix has kicked off a massive Xbox Live sale, discounting a ton of games at 50% off, some of which have discounted DLC. You'll find the list with links below, which consist of anything from Deus Ex: Human Revolution for $14.99, to Sleeping Dogs for $19.99 with DLC sales.
If I may make some more obscure recommendations, Geon is a lovely little puzzler and is easily worth $4.99. Lara Croft and the Guardian of Light is also a nice diversion (get the Raziel and Kain pack and support that IP!), and although Mini Ninjas isn't quite worth $14.99, it's still a decent bit of weekend fun if you have kids.
The great big Square Enix Xbox Live sale [Square Enix]