http://fits.gsfc.nasa.gov/fits_samples.html

File    Telescope/Inst 	Description
WFPC2u5780205r_c0fx.fits    HST WFPC II 	WFPC II 800 x 800 x 4 primary array data cube containing the 4 CCD images, plus a table extension containing world coordinate parameters. This sample file has been trimmed to 200 x 200 x 4 pixels to save disk space.
WFPC2ASSNu5780205bx.fits    HST WFPC II 	WFPC II 1600 x 1600 primary array mosaic constructed from the 4 individual CCD chips. (Image has been trimmed to 100 x 100 pixels to save disk space).
FOSy19g0309t_c2f.fits   HST FOS 	FOS 2 x 2064 primary array spectrum containing the flux and wavelength arrays, plus a small table extension.
HRSz0yd020fm_c2f.fits   HST HRS 	HRS 2000 x 4 primary array spectrum, plus a small table extension.
UITfuv2582gc.fits   Astro UIT 	Astro1 Ultraviolet Imaging Telescope (512 x 512) primary array image
IUElwp25637mxlo.fits    IUE LWP 	IUE spectrum contained in vector columns of a binary table.
DDTSUVDATA.fits Random Groups 	This example file illustrates the Random Groups FITS file format which has the keywords NAXIS1 = 0 and GROUPS = T. This format has been used almost exclusively for applications in radio interferometry and should not be used for applications outside of this field. It is recommended that new applications should use FITS binary tables to store this type of data. This example file comes from the Classic AIPS 'DDT' (Dirty Dozen Test) benchmarking suite.

Somewhat bigger FITS samples from the NASA homepage that are not included here because of the size:
EUVEngc4151imgx.fits    EUVE 	EUVE sky image and 2D spectra, contained in multiple image extensions, with associated binary table extensions. The 1st image extension has been rebinned by a factor of 4 to save disk space.
FOCx38i0101t_c0f.fits   HST FOC 	FOC (1024 x 1024) primary array image, plus a table extension containing world coordinate parameters.
FGSf64y0106m_a1f.fits   HST FGS 	FGS file with a 89688 x 7 2-dimensional primary array and 1 table extension. The primary array contains a time series of 7 astrometric quantities.
NICMOSn4hk12010_mos.fits    HST NICMOS 	NICMOS null primary array plus 5 image extensions (270 x 263) containing the science, error, data quality, samples, and time images
