I came across this nice posting wherein the author provides users with cool calculators for fluid mechanics applications.
Some of the calculations possible with this calculator include acoustic flow meter, bernoulli eqn, cavitation, cauchy formulation, darcy's eqn, manning effects, friction head loss computation, prandtl design calc, venturi -pump-water hammer effects..just to name a few....I would definitely like to bookmark such pages as they come in handy when I require quick estimation of flow parameters !!
Also, I found quite good fluid flow estimators with applets in the efluid site
Other websites containing such nice calculators for quick-off the shelf numbers....
Especially for venturi, orifice, pipe calculations
AOE.vt.edu/~devenpor/aoe5104/ifm/ifminfo.html - the famous ideal flow machine with online java applet
Combustion, Fuels - Thermal estimations
For compressible flow calculations
While initializing a domain estimations like hydraulic diameter, continuity, venturi effects are very important to obtain nice solutions. Ofcourse, one could make a big error in initializing and the solution can correct itself ..but how about providing a nice initial estimation - close to the actual numbers !