I would suggest getting all the EK books. You can buy them online. There are 2 different kinds of books, a review book for each subject (chem, physics, ochem, bio, there is also a verbal&math one) an the "1001" series which are books with practice passages that people say are very helpful. Again, there is 1001 physics, 1001 ochem, chem, and bio is coming out at the beginning of May. There is also the "101 Verbal" book which people say is the best for verbal prep; it is 11 full length practice verbals and its thought to be pretty representative.
It seems like the EK books are the most popular around here. Kaplan also has the big comprehensive book which you might think about buying. If you think you might benefit from audio style learning, EK also has some audio CD's called Audio Osmosis you can get.
In addition to the review books, I would highly suggest going to aamc.org, clicking on mcat, and getting some practice tests. The tests the aamc puts out are old mcats so they're obviously a help in getting a feel for what your test might look like. Right now there's aamc 1, 2, and 3 (but these are considered a little too old to be truly representative of the mcat of today), 4, 5, 6, and 7. You can buy them in paper or online format. AAMC 7 just came out. You pay $40 to get online access to it and can either take it at your computer or print it out as a pdf.
I don't think you need to take a prep course either. With some good materials and some motivation, you should be fine. I'm actually taking the mcat this august too without a prep course.
I'm using just what I mentioned above; the EK set, aamc practice tests, the kaplan book, old text books i'm sure somewhat and I also have the princeton review science workbook.
Good Luck!! Your scores the first time were not bad AT ALL, so I can't even imagine how much you'll rock the test this time with more prep.
...Oh, the last part of your question. Each practice mcat you take will be scaled a little differently for questions right to score because they factor a curve into the test. Once you get the practice tests or the books you'll see a break down of the questions to scores. I don't know it off the top of my head as I have yet to take a practice test except a couple verbal ones last summer but maybe someone else can help me out