To assist with the email not getting lost in SPAM traps etc, I've always used the from address as an address on the same domain as the web site. So for example firstname.lastname@example.org or email@example.com.
I then use the Reply Address as the email address entered by the customer in the form so that its easy to hit the reply button and get back to them.
So the To: address is the address where you want the email delivered (i.e. you)
The From: address would be an email address on the same domain as your web site
The Reply: address could be left blank or it could be set to the email address of the person that filled your form in.
If anyone wants to suggest otherwise feel free :-) but this is what generally works for me.