I don't have any nicknames that all my friends use, because there's not a lot you can do with Sarah...it's pretty basic. But here are a few that specific people have used:
Mrs. Hackbarth- OK, yes we are married...so it makes sense, but I received the nickname from our friends BEFORE we were married. They would always refer to the two of us as "the Hackbarths" or me specifically as "Mrs. Hackbarth"...good thing it worked out I guess! ;)
SarahLee- This one is definitely specific to one person. My friend Laura has called me SarahLee since high school and I always call her Scheetzy-baby (a play on her last name). I know we are getting older, and this might be a little childish, but I love it and I'm pretty sure we'll always use them as we grow old!
Sar-sar- Again, specific to one person. My friend Kelly and I were being goofy freshman year of college and I started calling her Kel-kel so she started calling me Sar-sar. And yes, we still use it when we call or text.
Pumpkin- I probably share this nickname with LOTS of little babies. But this is what my family called me when I was a baby/toddler, and I'm sure I'll call my baby someday the same thing. :)