Here are some of my favorite pieces of equipment:
1. Medicine Balls that bounce, such as these or these. Medicine balls that bounce have two advantages that I appreciate. First, they allow for more plyometric drills for the upper body and torso. Second, they can also train reflexes.
For sword martial arts medicine balls of 4lbs. or 6lbs are appropriate. The objective is something not more than twice the weight of the sword so that you can train speed of execution and the elastic properties of the muscle (with plyometrics).
For unarmed striking training a 2lb. medicine ball works just fine. For grappling training heavier medicine balls become more useful. But see the next item.
2. Sandbells are a great way to throw around heavier things. For these weights of up to around 30% of 1RM work well, since that is the resistance at which maximum power output occurs. Since these are used primarily for upper body work I base the resistance off of bench press 1RM. If you are buying these for a class then aim for lower on the weight, 10-20 lbs.
3. Weighted bars in two-handed and one-handed sizes are a great additional tool. And these are quite easy to DIY. A piece of iron pipe with caps, filled with sand (leftover from the sandbell project), works just as well. I, of course, recommend using them like swords i.e. holding them at the end instead of the way they are used in aerobics classes.
Also, as a DIY project you can make one-handed bars that are much thicker and heavier. These are then useful for grip and wrist strength.
I'm linking to the manufacturers website so that you can get the best view of the product. Once you know what you are getting you, I see no reason not to check Amazon for better prices.