Puppetswar is an online retailer based in Poland. I recently ordered a number of parts from them, including the Destroyer Arms, pictured below. Puppetswar make a range of resin bits for use with their own gaming systems, but they're very suitable for replacement parts for space marines and imperial guard style miniatures.
The destroyer arms themselves are great for terminator arm replacements. With a little work, they can also work for regular marines -- but the shoulders will need shaved down to take a normal shoulder pad on top. I think they'd make excellent alternatives to power fists, or even a close combat weapon.
The resin itself is reasonably well cast. There are minor issues, along the same lines as one might expect from certain other companies: minor air bubbles, flashes, and so forth. The poses are good with a variety on offer. And they also come with a small circular indentation on the inside so that you can place magnets in them to attach / detach from a torso.
My only complaint is the amount of time that they took to arrive: at the upper end of what they claimed on their website to say the least, but otherwise all good and well packed for the post. I'll be using these parts in my upcoming Alpha Legion army...