In one way, the Vikings are lucky.
They have the opportunity to bring in an elite prospect at two of the most difficult positions to fill in the NFL: cornerback and left tackle. In another way, they are unlucky because the roster has a lot of holes, which is why they are picking third overall, so they need to try to pick up extra picks.
It's not been easy for the Vikings to drum up trade interest so far, seemingly because the best player available is a running back; therefore, teams won't want to invest too much in that position. It is also difficult because the Vikings don't want to lose out on an opportunity to take Matt Kalil or Morris Claiborne.
The most likely possible move right now appears to be the Rams trading down with the Buccaneers, dropping them two places. They should still be able to grab Matt Kalil at that point but run the risk of the Cleveland Browns taking Morris Claiborne at fourth overall, presuming the Buccaneers take Trent Richardson.
Everyone is expecting the Browns to go offense with their first pick, but realistically Claiborne makes a lot of sense also. The Browns' high-ranked pass defense from last year is a myth that was created by teams simply running the ball on them all day instead of passing in competitive games.
I doubt the Buccaneers would be willing to give up their second-round pick this year, because it is essentially a first, so I would expect them to offer the Vikings next year's second rounder along with this year's first to make this deal happen.
Another option floating around for the Vikings to consider is potentially trading with the St. Louis Rams. The Rams have already traded back from second overall to the sixth overall pick but could be interested in jumping back up to third to grab Richardson ahead of the Browns and Buccaneers.
The Rams already have Stephen Jackson in the backfield, but he likely isn't going to be running too well by the time the team is relevant once again. Also, Jackson's contract is huge, and he isn't likely to re-negotiate it if he is to be playing with a rebuilding team.
Moving Jackson to a contending team would give him a career boost while also returning the Rams a mid-round selection, most likely a third rounder, to help them move up for his replacement. This deal swings completely on whether the team wants to move Jackson or not.
There should be plenty of teams willing to part with a third for the proven back; the Steelers, Lions, Ravens and Giants all come to mind as suitable partners, but separating themselves from the heartbeat of the team won't be easy.