Your Name and Company name (if applicable)
Contact info (address & telephone #) if applicable
Website URL
That is pretty much all an email signature should contain in plain text. Trust me no one needs to see a picture of your kitty or read a little ironic quote or quip in every email you send them.
I like to see an email address in the signature and PHONE NUMBER. personally I despise keeping an address book. I got into this habit in the early to mid 90s when every virus out there trolled your address book. I have for at least 15 years sorted contacts by received email. If I don't know you well enough to have your phone number in my cell, it could take me as much as half an hour to find your number. I *hate* it when idiot work people shoot a one liner "hey, call me I can explain this better over the phone please" and are not kind enough to list their number . . .