The StarCraft II beta is currently underway and already has us pining for the full release. As for exactly when that will happen, all we've known is that Blizzard plans to release the game in the first half of 2010. According to the latest BlizzCast, that's still the plan. During the podcast, production director Chris Sigaty stated that the beta should last "three to five months" and added that Blizzard is "still targeting the first half of this year."
With a three to five month beta window, that puts the end of the test somewhere between May and July. Of course, there's no telling how soon the game will release after the close of the beta, but hopefully it won't take too long. The universe won't save itself, after all.
Finally, for those out there lucky enough to be in the beta, you should know that the first patch is now available.