I like to do a variation of Giada DiLaurentiis' "all'Amatriciana"....the original features diced pancetta (which is also delicious - just more an *occasional* treat!

), but the sauce is also delicious without. I really like this one because I like my sauces simple, without a lot of extra "stuff" (though you could certainly add whatever you like), and it has a good kick from the chili flakes.
Basically, you just heat about 1 Tbs. of olive oil in a pan, then add a diced onion and cook over medium heat until the onion is soft. Add 2 crushed garlic cloves and a healthy shake of crushed pepper flakes, and saute until fragrant (about 30 seconds). Add in a 28oz. can of diced tomatoes (that you have pureed in a food processor until smooth), a pinch of sea salt and a grinding of fresh black pepper. Let it cook and bubble over a medium heat for a good 15-20 minutes, until the sauce has thickened and reduced.
For the original version with pancetta, simply saute about 6oz. of diced pancetta in the olive oil for about 8 minutes before adding the onion and proceeding as written above.
This is a great sauce over penne - I really like it with Barilla Plus. Enjoy!