What is this oddly-shaped plane?
It is the Airbus A300-600ST (Super Transporter) Beluga, which is a version of the A300 wide-body airliner modified to carry aircraft parts and oversized cargo.



Source: berlin-aviation-forum.com

The nose is shaped like that as the upper portion is basically a cargo hold and is used to transport oversize cargo, especially aircraft parts.



"F-GSTB - 2 Airbus A.300B4-608ST Beluga Airbus (8634655670)" by aeroprints.com. Licensed under CC BY-SA 3.0 via Commons.

The cockpit was lowered below the cargo deck so that the cargo area could be loaded without having to disconnect any of the vital electric and hydraulic lines running to the rest of the plane. However the A300’s lower fuselage, wings and landing gears were retained.

The following image shows the changes that were made in the nose section from A300 to the Beluga.



Source: allaboutguppys.com