How about all of the above? But if I do have to rate then its the lamp, loot detector (unless the script will be too heavy), ray and mines. throwing bombs would be cool too (yes I know there is already a mod for that, but still). All matter of soulgem powered gadgets would be cool, like maybe a spider-mount, stun-rays, mind-control helmets (the goofier the look the better), some sort of anty-gravity ray, telekinesis-like ray/spell to use on enemies and throw them down canyons and mountains, force-fields, shockers (electrocute in apocalypse, only in staff/raygun form), and don't forget flamethrowers and acidspitters (fuel could be made via alchemy).