I love
Simcha. I've always thought about it on a girl, but I could see it on a boy, too. I'm not Hebrew, but I'm pretty sure I could master a "ch," hehe. I think the name and interesting sound would stand out in a slew of more common names.
Tamar I've never heard of. I love
Tamara. But I like the idea of
Tamar. I don't think I would use either, but they both sound and look nice.