http://msdn.microsoft.com/en-us/library/bb197848(v=XNAGameStudio.30).aspx
ContentManager.Load Generic Method
The type of asset to load. Model, Effect, SpriteFont, Texture, Texture2D, Texture3D and TextureCube are all supported by default by the standard Content Pipeline processor, but additional types may be loaded by extending the processor.
Before a ContentManager can load an asset, you need to add the asset to your game project using the steps described in Adding Game Assets to Your Game.
The following are the Content Pipeline run-time classes supported by Load and the file formats they are associated with.
| Effect Class | .fx |
| Model Class | .fbx, .x |
| SpriteFont Class |
.bmp, .spritefont, .dds, .dib, .hdr, .jpg, .pfm, .png, .ppm, and .tga  Note The default content processor for .bmp files is the texture processor. To process a .bmp file for use as a Sprite Font, click Sprite Font Texture – XNA Framework in the Properties pane for the .bmp file after it has been added to the project.
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| Texture Class, Texture2D Class | .bmp, .dds, .dib, .hdr, .jpg, .pfm, .png, .ppm, and .tga |
| Texture3D Class, TextureCube Class | .dds |
Note that these are the formats of the original assets; after processing, all assets will be .xnb files.