I think most people with a high school education can handle reading straight from St. Thomas. I highly recommend Peter Kreeft's abridged and well-annotated version Summa of the Summa. He has a gift for making the more difficult ideas of Aquinas easier to understand.
A podcast geared towards Aquinas without being too technical is Pints with Aquinas by Matt Fradd.
I read Peter Kreeft's Summa of the Summa. It's literally the philosophical part of the Summa, but Dr. Kreeft edited out of it objections, articles, etc. that have little to no relevance today--so it's only about 500 pages long instead of the full length monster that it is. Also, Dr. Kreeft filled it with comments (in the form of footnotes) to the brim, actually quite helpful when getting through the heavy handed stuff.
Peter Kreeft has two books that sound like what you’re looking for:
A Summa of the Summa https://www.amazon.com/dp/089870300X/ref=cm_sw_r_cp_api_glt_fabc_XEH1RJPWDDA3CQM9NDGQ
A Shorter Summa: The Essential Philosophical Passages of Saint Thomas Aquinas' Summa Theologica https://www.amazon.com/dp/0898704383/ref=cm_sw_r_cp_api_glt_fabc_VQ1K1DK7ZTD76FN0QT5G
You are welcome! Here is the link to the one I read because the originals are difficult to jump right into.
https://www.amazon.com/dp/089870300X/ref=cm_sw_r_cp_awdb_imm_JPEQM0GXMQ0F0MKRW636
Maybe with start with the "Summa of the Summa" by Kreeft:
https://www.amazon.com/dp/089870300X/ref=cm_sw_r_tw_dp_U_x_XpLpCb8GEVP7F
Otherwise its difficult to know where to start with the whole summa.
The Summa Theologica is not a good place to start. You're better off getting the Summa of the Summa.
http://www.amazon.com/Summa-Thomas-Aquinas/dp/089870300X/ref=la_B000AQ3SDK_1_2?ie=UTF8&qid=1349311066&sr=1-2 this is some thomas aquinas, arguably on of the most important people in Christian history than the Big Guy. he was a dominican in medieval europe
this is by C.S Lewis, who wrote the chrinicles of narnia. he is also famous for converting from atheism to christianity. he explains chrsitianity, and justifies it in simple terms. http://www.amazon.com/Mere-Christianity-Gift-C-Lewis/dp/0061350214/ref=sr_1_1?s=books&ie=UTF8&qid=1349311217&sr=1-1&keywords=mere+christianity