Rotobrush in after effects CS5, but it apparently doesn't work that well with anime, so manually masking them is still the best choice, not only for quality, but for speed too (fixing them around ends up taking as much time, according to people who tried to use rotobrush on anime).
Imho, you just need to get a hang of masking. Here's some tips:
- Lay as few vertexes as possible and properly set the bezier to follow the lines. Anime have generally simple shapes, perhaps hairs aside, so instead of following the whole thing and laying a vertex every 2/3 pixel straight, you could save time and have a better quality mask by just doing like so;
- Don't redraw the vertex every frame, but just move what needs to be moved. Refer to the next point to make this easier and faster, and probably more meaningful;
- Separate the image into "parts." For instance, have a layer for the hand, another for the body and so on. In some cases the animation only really changes in some bit of the image, so this way you might be able to save some time. You'll also be able to have much more control over the mask if you by any chance need to do any morphing or whatever. Also, keep in mind that moving a few simple vertexes around in a small image is much easier and safer than moving many in a complex one: for instance, if you fuck up while moving the vertex in the whole image, fixing up everything might take a bit of time (ok, not: you can just go "back in time" with ctrl+z, after all, duh ), but if you have simple shapes, it's much easier to just move around a couple things. Think of this example: you have the character moving the arm, but the hand is in the same shape and is only moved around, and the rest of the body is still fixed (things like this happen a lot in anime, if you think about it) ─ you will just change the mask of the arm, and then just shift around the mask of the hand, maybe without even having to fix the single vertexes.
I know some of these might take a while to get accustomed to, and might not be worth if there's only a few images to do (I know I don't really do the second and third thing myself), but if you have a lot of things to mask like you said, then in the long run, this will speedup and improve the quality of your masks.