The Galton papers and effects are housed at University College, London. Over 10,000 items are housed there, including manuscripts, letters, diaries, newspaper clippings, the fingerprint collection, Galton's "toys" (the many instruments and devices he experimented with) and other ephemera. The collection now has a website, which includes some interesting digital images.
The collection of papers has been catalogued in a booklet, but there is no electronic catalogue with sufficient detail. The booklet (browse page images) has been made searchable here, to aid research. There is also a printed catalogue of his instruments.