Below are profiles on 2 veteran Japanese relievers that are free agents (and can be signed by American teams) that I find somewhat interesting.
Shinobu Fukuhara is a 35 year old reliever who dominated in 2012. The right-hander flamed out as a starter and was eventually moved to the pen, where he has seen a velocity increase and has been more successful.
You can see Fukuhara throw over 91 MPH in this video.
The velocity is under average, so he will have to make up for it with pitchability. The forkball in the video is really inconsistent. Some of them are not very good, and others act like excellent splitters. He seems to really like the pitch, going to it often. It does seem to be something that he keeps low. He doesn't seem to throw the curve much, and he could probably do without it, as it doesn't seem to be a very good pitch. If the pitch F/X is right, he added a changeup this year as well, but I don't see it in the video. I like him best of the two pitchers, but whether he is a MLB quality pitcher or not relies a lot on his forkball.
Ryuji Yokoyama is a undersized 36 year old right-handed reliever that has pitched for the Hiroshima Carp for years:
Here is a video I found that shows Yokoyama throwing, so you can see his mechanics and pickoff move.
He made 65 million Yen last year which is roughly 810,000 dollars in American money. So the question would be whether or not he is worth that much (and a roster spot) in the Majors. With that kind of salary, you are only asking him to be slightly better than replacement level, possibly 2 to 3 runs more. That is roughly asking for a 3.90-4.10 FIP/ERA (if he throws a "qualified" amount of innings out of the bullpen, which is around 50 innings. He threw exactly 50 innings in 2010, so he would probably be 3.90 ERA/FIP or better, as he probably isn't going to get that many innings).
I don't know if you can expect that for Yokoyama. I like big fastballs or sidearmers in bullpens, and while there have been pitchers that don't fit that description that have pitched well in a MLB bullpen, I usually have to see it to believe it. Yokoyoma was really good before the ball change in Japan, but this year's K/BB wasn't actually very good, despite the dominant ERA/WHIP. It would be a low risk signing, and he has to decide that he wants to play in the Majors anyway and not stay in Japan, but I doubt I would pursue Yokoyama very much if I was a MLB team (especially if I had to guarantee him salary and a roster spot, and I have no idea why he would come to the States on a non-guaranteed contract).