I bought a Sammy that has a vibration in the transfer case up to 25 mph.  Do the transfer case arms come in one size fits all?  What brackets/arms/mounts would you recommend and why?

All the Sammy's have the same t-case mounts.  You may want to pull your t-case off and see if the long mount has been twisted up.

As for after-market kids I am a fan of the Snatch from ZOR.  One of the guys in the club just picked on up and it is one of the few that make removing the t-case easier then stock due to it's design.  But you really can't go wrong with any of the products out there.

You might also want to check your u-joints and bolts on the jack-shaft between your t-case and the transmission.

check the drive shaft bolts, u-joints and the get under the vehicle and push up on the t-case. the mounts break all the time. Look at the rear tranny mounts...it's very weak too and can cause some vibs.