Depending on your definition of difference maker, there are a few in this draft. The easiest one to mention is Andrew Luck. Considering he will likely go to a team like the Dolphins who are a good QB away from being a decent team, his appearance could be a huge difference to that team.
However, there are other difference makers at other positions. Like Matt Kalil at left tackle. Do you know what he could do for a team like the Colts? Picking him makes the Colts offensive line infinitely better in an instance. They will have invested 2 first round picks, and a second round pick in their line, leading to a young, talented line to help Manning in his Twilight years and gives whoever the future QB is two bookend tackles.
There's also Justin Blackmon. Could you imagine a world where Sam Bradford has Justin Blackmon? The NFC West would be theirs for a while. Blackmon is a freak of a receiver, and with the passing ability of Bradford, that passing attack could go from abysmal to good with just one addition.
Also, there's Trent Richardson. He has been a beast doing the same thing his predecessor, Mark Ingram, did. Power running, running over everyone on the field, and just plain beasting. Running backs are usually players that succeed in their rookie years since the progression from college is somewhat minimal. If he goes to a team in need of a good running back, like say Denver, he could really shake up that running game and be a good crutch for a developing QB (cough cough Tim Tebow).