The key references for thermophysical properties data are as follows:

Books

Thermophysical Properties of Matter data series, vols 1-13, eds Y S Touloukian and D P De Witt, IFI/Plenum, 1970.

Somewhat dated but still a key source of thermophysical property data; separate volumes cover thermal conductivity, thermal diffusivity, specific heat capacity, thermal radiative properties, viscosity, thermal expansivity and other properties of solids. Each volume has useful introductory pages on the theory and measurement of the property concerned.

Recommended Thermophysical Properties for Selected Commercial Alloys, K C Mills, Woodhead Publishing Ltd, Cambridge, England ISBN 1 85573 569 5 (2002)

A critical review of available data (heat capacity, density, viscosity, surface tension, thermal diffusivity and thermal conductivity) of selected elements and alloys, aimed at providing the solidification modeller with critically reviewed data. Contains recommended property values with an indication of uncertainties of measurement. Included are aluminium, cobalt, copper, iron, magnesium, nickel, silicon, titanium and zinc and some selected alloys.

Websites

http://amptiac.alionscience.com/ProductsAndServices/:
Advanced Materials & Processes Technology Information Analysis Center - access to the properties database is Windows-based and user-friendly. Easy to follow set-up and operating instructions are included in the user manual. The database is also available on CD-ROM. Also publish a newsletter on materials technology developments; has links to US companies and organisations.

http://www.ike.uni-stuttgart.de/dienste/tp/thermophys_e.htm:
THERSYST thermophysical properties database on solids combining data from measurements in the IKE laboratories and from research of the scientific literature.

http://www.gi.rwth-aachen.de/forschung/rechner/dienste/mebsp-b/main.html:
MEBSP thermophysical property data for casting simulations (Microstructural Engineering By Solidification Processing - MEBSP) and other information and resources, including links to other databases relevant to castings simulation.

http://www.ashrae.org:
The ASHRAE Handbooks on heating, ventilation, air-conditioning and refrigeration (HVACR) are published in a series of four volumes, one of which is revised each year, ensuring that volumes are kept up to date. The volume on Fundamentals covers basic principles, data for HVACR design, refrigeration cycles, fluid flow, heat and mass transfer, farm crops, air contamination, odours, measurement and instruments, airflow around buildings, energy resources, fuels, refrigerants, desiccants, thermal and moisture control and vapour transmission, ventilation, infiltration, heating and cooling loads, fenestration, space air diffusion, duct design, and pipe sizing. Also includes controls, building envelopes, and physical properties of materials. Available via the website or as a book.

http://www.ppds.net/help/h_Introduction.asp :
An application for determining the physical and transport properties of fluids and fluid mixtures.

Details of Thermal Measurement Services can be found at Thermal Performance.