President Obama will address the nation in primetime at 9pm ET, Monday night (presumably about the budget crisis). Look for all the major English language broadcast networks, as well as the cable news networks to carry the address. I haven't seen the schedule change details yet other than Fox, whose head of scheduling tweeted the details: a new Hell's Kitchen would air at 8pm and that a repeat MasterChef would be joined in progress after the 9pm address.
Update: ABC will re-join primetime programming (“The Bachelorette”) at the same point it was interrupted by the special report. The start times of “Extreme Makeover: Weight Loss Edition,” late local news, “Nightline” and “Jimmy Kimmel Live” will be pushed later.