Very simple, like below,
Dear USCIS officer,
May I follow up the current status of the I-485 application of me and my family?
Our case numbers are,
SRCxxxxxxxxxxxx
SRCxxxxxxxxxxxx
SRCxxxxxxxxxxxx
Our cases were received on 5/21/2013 and provided figure print on 6/21.
Thank you very much for your help and have a great day.
xxxxxxx
mine is TSC so got the email address from Pjiang's blog - tsc.ncscfollowup@dhs.gov