Hi,
I had a similar question last earlier this year, here is the thread (with pictures of some popular options). I also looked into the stainless steel Mustad Crimpers mentioned that are pretty new out, Mustad actually got one of their senior European guys, an Italian, to respond - presumably because he is more familiar with spearfishing; the upshot being that it should be good for crimping/swaging spear lines.
Here's a link to that thread:
http://forums.deeperblue.net/diy-hom...spearline.html
...and another:
http://forums.deeperblue.net/speargu...ne-needed.html