Of course, my first suggestion would be the Summa Theologica itself, but for some odd reason, I think that the $250 price tag and the 3000+ pages might scare a few off.
So I recommend Summa Theologiae: A Concise Translation by Timothy McDermott. I believe this was my introduction to the Summa Theologica as well, although at this point I can’t remember for sure if it was the Summa of the Summa, or Shorter Summa, or A Tour of the Summa, or what I first looked at.
Among these, however, I have to recommend the Concise Translation the most. The others are, no doubt, good introduction, and shorter than the Concise Translation, but if you want to get the most for the least, fully fledged Thomas yet readable (although it isn’t a “breeze through the Summa,” for nothing could be) then I would go with the 650 page Timothy McDermott book.
As one reviewer accurately stated:
For those of us who do not have the time to physically sit down and read all five books of the Summa, this is most certainly the closest you will come to consuming the real thing! I found this after I had began to read the first few chapters and nothing comes so close to capturing the essence of Aquinas’s writings so thoroughly (and in only a sixth of the size of the original)! This book is a must for the true Thomistic scholar!
Two quick notes:
1. I will try to offer book suggestions from time to time, mostly toward learning the truth that is Thomism. However, it should go without saying that anyone following this site (Is there anyone?) should be reading the Holy Bible and praying above all else.
2. I don’t necessarily endorse Amazon.com, but they are convenient for showing books, and I can’t imagine their being upset since it’s a constant advertisement for them.