One guy I'd be interested in with the second pick (but probably won't be available after mid teens) is Corey Brewer of Florida. He's skinny (6'9" 185) but very long, athletic, and a good passer. He's not much of a shooter, but scores in transition and on drives to the basket.
So why Brewer? He has the reputation for being the best perimeter defender in college today. Whenever I see him, I think Tayshaun Prince. I could see him as a defensive specialist and possible long term replacement for Marion.
The need for another lock down defender cannot be overemphasized. After Marion and Bell, the Suns don't have anyone else capable of dealing with great offensive opponents. Injuries and fouls can be huge problem.
More important, neither Marion nor Bell are all that long. Having someone off the bench who is tall enough that Dirk, Kobe, Ray Allen, etc. cannot just shoot over would be a huge plus.
Brewer is not likely to last into the 20's, so I'm guessing the Suns would have to trade up to get him.