I put myself in time out when it gets too bad.

I tell my girls that Mommy is in time out and no one can talk to her until the timer rings. Since they know they get in trouble when they talk during time out they actually leave me alone.
Of course it only gives you 1-3 minutes of quiet time,

but there are days that that is all it takes to calm down and refocus on how to get them doing something on their own.
I have also turned my ears off for periods of time before.

I let them talk away to me and simply don't respond. It took awhile for me to be able to do this, but after a few times if me basically ignoring them, they learned that they need to be quiet for a while or Mommy will have her ears turned off for a long time.
Otherwise, I am a big fan of sending them out to run around the yard ___ times (as many times as they are years old) . Then they have to do either sit ups or jumping jacks or just jumps while they count to some number. A bit of physical activity seems to get their brain working on its own and then they don't require as much attention when they get back in.
I've also actually phone a relative or friend and made them ask their question(s) to who ever is at home on the other end of the line. It gives me a break, the grandparents a chance to talk to them and be involved in their latest obsession.

Not to mention giving them an idea of what we actually go through most days.