After the debacle with the slotting of bonuses in the 2007 draft, Bud Selig really pushed for teams to draft players they wanted, not that they could afford, as it pushed so many guys to large market teams, which is antithetical to the whole slotting system. With that being said, guys who dropped because of signability was really reduced this year to the barest of minimums. However, guys who did drop included Tim Melville, who was considered a 1st round supplemental pick, at worst, and fell to the 5th round and was selected by the Royals. Not really many other guys of note at the positions you are looking at, but guys who could become MLB productive players include:
Roger Kieschnick (3rd round - Giants)
Isaac Galloway (8th round - Marlins)
These guys come to mind as good values. Kieschnick drafted in the 3rd not because of signability, but Galloway is a guy that fits the profile you are looking at, in terms of talent, as he was looking for more money than his slot would indicate.