Yeah someone was looking for a full name that shortened to Hattie a few days ago, and she settled on Tabitha! I must say it's my favorite of the Tabitha nicknames. I like Tib and Tab better than Tibby or Tabby. Or how about Tay? Tae, if you want to be really artsy. Other options: Bitha, Bithie, Bitzy, Betsy, Betz, Bitz.
The person who was looking for a full name with nickname Hattie is me!:) So far I almost decided on Tabitha and, of course, I think Hattie is the best nickname for it. Other ideas: Tata, Bitha, Tab, Bee, Ita, Abby. Tabby reminds me of Beatrix Potter books so I find it lovely, but not very appealing on grown-up, though it's incredibly cute on baby.