A bog-standard Sword +1 is a boring blade indeed. Here are a hundred extra features to make a magical weapon more magical than just the basic bonus.
These are largely system neutral, but feel free to season to taste. If anythings unclear, go with your gut or feel free to ask and I can try to explain my thinking in a less intentionally terse format :). Let me know how your players respond to these, and if you think it might be worth trying to put together separate tables for other types of weapons.