There are a few options for Shockwave. The first is Energon Shockwave, who is a nice-sized figure but his arms are not all that well done.
The second is obviously this figure. He's a nice figure but in most collectors oppinions, it's too small to be a good Shockwave on a classics-style shelf.
The third is the recently-seen TF: Prime Beast Hunters Shockwave, who looks pretty good, but we really haven't seen too much of him yet. Apparently the red spiky armour can be removed.
Finally, if you wish to be patient, there is going to be a voyager-sized release of this guy
, currently Masterpiece-sized. However he won't see release until 2014.
I would suggest waiting either for Prime's Shockwave or the 3rd party one unless you can get FOC Shockwave for really cheap.