Any good recommendations for a download Accelerator which works well
with GOG?
I have tried Gigaget and failed

I use DownthemAll for Firefox, works pretty well.

I use Free Download Manager, which is of course free. :) It works perfectly.
Note that for any download manager other than GOG's own you will need to feed in a new source URL any time the download gets interrupted. Some download managers will automatically add the new URL to the download as soon as you send it to the program while for others (such as Free Download Manager) you will need to copy the link from the new download window that appears and add it into the old one yourself. Regardless of the method required the end result is that you can pick up from where the old download left off.

Thanks a lot!