Today's name is Theresa, which comes with the cute nicknames Tess, Tessa, Terra, or Reese/Reesa. There's Terry and Tracy, but they've fallen out of favor and seem dated. Theresa is Greek, meaning "late summer, to harvest (which is synonymous with to reap/gather)." It's most famous namesake is Mother Teresa, and what a great person to share a name with, although there were two other saints with this name. Theresa is teh-REE-sah, but you could also opt for Terese/Therese, said teh-REESE.
The first known namesake was the Spanish wife of Roman nobleman Paulinus from the 5th century. Apparently she was a writer who other women were fond of, thus giving her name to their children.
Here is a lovely list of international variants: wikipedia
Looking for something a little more unusual? Try Theria, which may have been a variant at some point, as both Theria and Theresa may come from the name of the Greek island Therasia. Theresa reached it's height around 1960 and is no longer on the top 1000 as of 2010 when it ranked at #928, a slow decline over the decade. Still, it is just below #1000, having 211 births in 2011. That being said, I don't see it coming back into the top 1000 any time soon, as Tess and Tessa have taken over with their similar, yet more modern sound. Tess in 2011 was #925, on its way up, and Tessa was #229, sort of hovering around that spot since 2000.