As someone currently planning a wedding, I can tell you -- anything off of your sister's registry would be fabulous! Even the most mundane things are special to me because I know that someone took the time to look up what we needed/wanted before they made a purchase.
One of my DZ sisters who just got married received a TON of engraved picture frames and things like that -- which are all really nice and definitely wonderful keepsakes-- but she could have used things from her registry more (like her everyday dinnerware).
Don't get me wrong... I feel that any gift is ALWAYS appreciated. However, with a registry gift you just can't go wrong.
Good luck!!