WR is right on for this one.
I've been dating a girl 20+ months (will be 21 on the 13th) and the bear definitely is a hit.
Before we went to college we went to the Create-a-bear place and made each other a bear to remind one another or the other while away at college.
I wouldn't do jewelry after 6 months, but if you decide that's the best route, I'd get her a necklace that has to do with her birthstone and maybe have that set in diamonds, but that's going to be costly, especially since it is only 6 months. Girls don't often wear the same earrings on back-to-back days and rings are reserved for far more important relationship dates. Some girls don't like bracelets...definitely, if you get jewelry, make sure it's a necklace.
But, personally, I'd do the bear because it gives her something to cuddle at night when you aren't there and you can personalize it (even give it a sound bite when you squeeze its hand) that can remind her of you; always a plus.
Hope that helps...and p.s. what should I do for Christmas for those that have been in relationships close to 2 years. Money isn't really an obstacle here so play whatever ideas you have (keep them somewhat realistic, though).