My friends and I are going to Madrid from the US and we have a stopover in Brussels from 8am till 2pm on a Sunday morning. Are there any suggestions for a nice and feasable place for brunch or breakfast? Or somewhere interesting to kill some time that we can get to from the airport easily? This is our first trip to Europe.

Will you have the entire time from 8 am to 2 pm free? Or is that the time your planes arrive and depart? In which case, you'll have a lot less time.
I suggest you take the airport train into the Gare Centrale, then walk over to the Grand'Place and from there up to the Sablon for breakfast (or do it in reverse order if you want to eat first). On the Sablon, one of the prettiest spots in Brussels, are numerous cafes and a branch of Le Pain Quotidien, which has great breakfasts. You can also browse the antiques market set up in the square, walk through the little garden at the top end. There is an international press shop on the corner if you want to grab an English (or other) language newspaper. If you read French, pick up a copy of La Derniere Heure newspaper and read about all the strange doings in this small country. (And I do mean strange.)
In that amount of time, you'll have seen two of the prettiest/grandest parts of Brussels (Sablon/Grand'Place), had a nice breakfast and a brisk walk, and still give you plenty of time to get back to the airport.
FYI, if there are more than two of you, you could split a cab to the GP or Sablon...would cost about 30 euros each way, or 10 euro pp if there are three of you. The train is about 6 euros RT per person.

Thanks for the great info. We should arrive at 745am and leave at 1230pm. I printed the wrong time before, so there is less time than I thought. There are 3 of us, so maybe we can make it in time to eat.

I was about to recommend practically the same thing as BTilke. The Sablon is a great place to spend a Sunday morning. If you have time, pop into Pierre Marcolini's (at the bottom end of the Place) and stock up on some wonderful Belgian chocolate. The store - with its black velvet decor - is an experience in itself!

So...you would probable be free to leave about 8:30 and would have to leave central Brussels about 11. That only gives you two full hours plus some change (and only if you will already have your boarding passes for the flight onto Madrid). You can still visit the Sablon/GP, but forget the airport train. Take a cab to the Sablon (should get you there in 15 minutes), have breakfast at Le Pain Quotidien (if they are completely full, try the cafe inside the Flamant home design store, Au Vieux St. Martin or Wittamer's across the square), finish breakfast by 9:45 am, give yourselves half an hour to stroll around the Sablon, walk down to the GP (15 minutes from the Sablon), give yourselves a good look, then catch another cab back to the airport. There are taxi stands near the GP, one by the glass covered galleries (pretty sure; if not reception at the Novotel there can tell you where the closest one is), one by the Bourse, and a little farther out, one in front of the Metropole Hotel by de Brouckere. Definitely be back in a cab by 11 am, so you're at the airport by 11:30 am at the LATEST, giving you enough time to go through passport control, get to your gate, etc., without rushing like maniacs.