I thought I'd add a different sort of favorite 'tool' to the mix. I find piecing so much easier when I have some Kwik Sort on my fingers.
http://www.leeproducts.com/Sorting_Sortkwik.aspx
It's the pink fingertip moistener used when you handle a lot of paper.
I find it very helpful when trying to line up 2 pieces of fabric to pin and stitch in place. I keep small containers of Kwik Sort next to my machine, in my Tutto rolling bag for when I sew away from home, and in with EPP supplies. It's a little inexpensive tool that makes all the difference in the world for me.