Image Eye can read a whole lot of different file formats:

Ext.Format description
APNGAnimated PNG.
BBMDeluxePaint brush.
BMPWindows bitmap format.
CURWindows cursor.
DDSDirectDraw surface.
DIBWindows device independent bitmap.
FITFlexible image transport system.
FITSFlexible image transport system.
GIFGraphics interchange format.
HDRRadiance RGBE image format.
ICOWindows icon.
IFFInterchange file format.
IMGRadiance RGBE image format.
JIFJPEG image file.
JPEGJPEG format.
JPGJPEG format.
LBMDeluxePaint bitmap.
PCXPC Paintbrush image.
PICRadiance RGBE image format.
PNGPortable network graphics.
PSDPhotoShop format.
RLEWindows RLE compressed bitmap.
SUNSun raster format.
TGATARGA format.
TIFTag image file format.
TIFFTag image file format.

Write support however, is limited to BMP only. If you want a format converter, then check out Any Image - which besides additional write support also reads several less common formats!