There's a really good article in this past January's Modern Steel Construction magazine, published
by the AISC titled Are You Properly Specifying Materials? Here's the link to the online version:
http://www.aisc.org/Content/ContentGroups/Modern_Steel_Construction3/January_2004/30725_materials.pdf
It has ASTM specifications and information for most everything used in structural fabrication.
It covers W, M, S, HP, C, L, WT, HSS, plate, all types of fasteners, anchor bolts, etc. Definitely worth checking out.
jsimon514: HSS is available in rectangular and round in the commonly used ASTM A500 Grade B,
but are also available in ASTM A500 Grade C and ASTM A501, which are all carbon steel. In addition, HSS rectangular and round are available in ASTM A618 Grades 1,2, and 3, which are high strength low
alloy steel. Rectangular HSS is available in ASTM A242 and ASTM A588, which is corrosion resistant high strength low alloy steel, and rectangular and round HSS are available in ASTM A847, which is corrosion resistant high strength low alloy steel. The charts on the link provide tensile and yield properties, which may assist in your calculations, if you know the material grade.