It may not be the Summer of Arcade until mid-July, but it's going to be a good summer for XBLA even before then. In a list of upcoming Xbox Live content, Microsoft announced that Derek Yu's long-awaited Spelunky will be out July 4, for 1200 Microsoft Points (alongside Bellator MMA Onslaught).
Other upcoming Xbox content of note includes, of course, expansions to Skyrim and Mass Effect 3, along with Battlefield 3: Close Quarters, all out today. Later this week, XBLA will host Jeremy McGrath Offroad Racing and Mini Ninjas Adventures.
As for deals, this week (through July 2) offers a random grab bag of multiplayer-focused XBLA games at various discounts, including Trine 2, Gotham City Impostors, Worms 2 Armageddon, and a heavily discounted (75% off) Nexuiz.