Wavemaster
Wavemaster, the new standard in martial arts bag training. Way more convenient than traditional hanging heavy bags, I haven't been to a dojo recently that didn't have a bunch of these. This one's the original and the one I have in my own back yard. It's held up extremely well, of course, I store the top indoors when I'm not using it and leave the base outside. I really like these over the old hanging heavy bags. Those are ok for punching, but they tend to get bottom heavy, and I really screwed up my ankles kicking them. I give this bag four kiai.

Powerline Wavemaster
Much thicker padding than the original Wavemaster, and if you're a powerful kicker, this is your bag.  I have decent kicks and I tended to bottom out and strike the center support while kicking the original Wavemaster.  These Wavemasters are so thick, I can't imagine getting all the way through this pad.  Although I prefer the realism of the BOB bags, this is the best bag for increasing the power of your kicks. I give this bag five kiai.

BOB XL - Body Opponent Bag - Full Torso
Truthfully, I don't own this bag and we don't have one in our dojo. This review is based primarily on my desire for this bag. I have wailed on it in the Sports Authority, and then quickly walked away before the sales staff came. The above bags are good for working on your power, but this bag allows you to work on the precision of the strikes as well. Granted, it's not moving, but definitely calls for more accuracy than a big red bag. Because I really, really want it, I'm giving it five kiai.

(Addendum)

I now own BOB.  I chose the Full Torso version so I could work leg kicks.  BOB is everything I had hoped.  I quickly learned that techniques I took for granted needed some tweaking if they were to reach the intended target area, and that is the value of a realistic striking dummy.  Not only that, BOB is built to look like a tough fellow (despite the lack of arms) and his appearance brings up the level of training.  BOB is stiffer than the Wavemaster Bags so you might have to adjust your kicking somewhat.  Owning BOB has not changed my rating, and he remains a very solid five kiai.

BOB - Body Opponent Bag
This is the original BOB.  He's still really fun to beat up, but because it's not full torso, all strikes must be above the belt because, frankly, there is no below the belt.  Of course, this is only important when training for self-defense or matches where leg kicks are allowed.  Original BOB is cheaper than BOB XL, and he's probably a better sparring partner for sport kumite because you can't work illegal strikes and develop bad habits, but other than that I prefer Big BOB.  Little BOB still gets a respectable four kiai.

Bobby Bully
This is the kiddy version of Bob. And as much as I like Bob, I'm not sure if I want my child with the imagery of repeatedly hitting such a life like bag. If your child is timid, this might help them get over their fear of bullies, but otherwise it might send the wrong message. All in all, I think one of the regular standing bags would be more appropriate for children. Because of this, I give Bobby three kiai.

Kid Kick Wavemaster
This bag is probably more appropriate for children. I don't believe young children should strike bags too hard because of their developing joints. Because of this, the thickness of the bag shouldn't really matter. So, even though there are heavier children's bags, if your child complains that the bag isn't thick enough, then they're probably hitting it too hard. This bag gets four kiai.