We had the last ranked defense in the league last year, a DE would be the biggest upgrade to that, followed closely by a CB.
Anthony gozalez, jason hill, and sydney rice are all probably going to be there in the second, so the second round pick would be the one to go for a good WR.
As far as a RB, Lendel was second string last year so this is his year. I would not be suprised to see us take a RB possibly in the 4th, were you could pick up a lorenzo booker or Kenny irons type of guy, ive even seen Michael Bush projected in the 4th, but he probably wont be there when we pick