Out of the box, GeoServer supports a good range of raster formats, and for the majority of use cases, the standard supported formats are, most likely, all you will need. The standard formats supported by GeoServer Version 2.5.2 are:
ArcGrid: The ArcGrid coverage format (http://en.wikipedia.org/wiki/Esri_grid)
GeoTIFF: A tagged image file format with geographic information (http://en.wikipedia.org/wiki/GeoTIFF)
Gtopo30: The gtopo30 coverage format (http://en.wikipedia.org/wiki/GTOPO30)
WorldImage: A raster file accompanied by a file that contains geo-reference information
It is likely that the vast majority of raster data that you will use with GeoServer will be in GeoTIFF and/or WorldImage (for example, TIFF files with an accompanying TIFF world file). However, there might come a time when you need to serve a nonstandard raster format through GeoServer, for example, MrSID. Luckily for us, these fringe...