Google also does conversions. Just type into a Google Search Bar (at www.google.com or in a search bar in Firefox, say) the conversion you want. The syntax is xx original_units in new_units. For example type in
10 m/s in mi/hr
and it responds with
10 (m / s) = 22.3693639 mi / hr
or
10 furlongs/fortnight in m/s
gives
10 (furlongs / fortnight) = 0.00166309524 m / s
Yes, it rounds strangely.
The calculator can do simple arithmetic, knows some physical constants, and it can combine unlike units. See <http://www.google.com/help/calculator.html> For example it can resolve
3 m/s + 3 mi/hr
to 4.34112 m/s. You can also get it back in m/s by asking for it that way