UNIT CONVERSION
http://www.digitaldutch.com/unitconverter/
This site has a very intuitive interface and covers just about anything a lab scientist might need. You can also change the number of digits that it shows. However, it doesn’t show you the equation it is using, so you can not use it to eventually gain independence.
MICHAELIS-MENTEN
Michaelis-Menten Grapher at Physiology.Web
Physiology.web often has very useful calculators and explanations. Their interactive Michaelis Menten equation grapher is a very nice way to explore what can be a difficult concept to grasp.
This size has some great explanations of statistical concepts. Highly recommended.
CONVERTING BETWEEN RPM AND RCF
http://insilico.ehu.es/mini_tools/rcf_rpm.php
This is very straightforward – input your RPM and your rotor radius and voila. It even shows you the equation it uses.