Hi all
Here is the protocol that I use routinely in the Lab I am using mainly two types of cell lines COS-7 and BHK.

Freezing Medium:
10% DMSO
20% FBS
Growing medium (in my case either DMEM or DMEM:F12 )

Trypsinize the cells
Spin down cells (1000rpm 2min)
Aspirate the medium
Add 2ml of freezing medium(per 1 10cm dish)
Pipette up and down the cells
Immediately transfer 1ml to cryo-tubes

Put in -80deg Celsius