As much as I like Markakis, he had some ugly stretches this year, and OF is replaceable even with separated out RF. As much as I like Sandoval, he's only a 3B next year, and his numbers are going to look a lot worse there than they did at C this year (for us Yahoo! users). Hunter is 74 years old and coming off of injury. Lackey seems a little off.
Phillips is still a credible stud at a thin position. Votto's a comer, and even though I have him as the most replaceable of the 4 I've recommended keeping, he's got some nice upside. The two pitchers should give you a great foundation. Wainwright was nearly a Cy winner this year (assuming he doesn't pull of the upset), and Santana's surely got one more super duper nice year.
If I upgraded through trades, it would be to get a better hitter to replace Wainwight (whom I would try to trade after that year) or to upgrade Votto, who might be a little underpowered to be your 1B (I like him more for UTIL).