I have merged laser+prism, doll+box, plate+polish, is there any more items that can be merged, also my ranger can do some alchemy now so does he just merge potions.

There are plenty of items can be merged. :D What you need to do is periodically try to have your gadgeteer merge every new gadget part that's found with the other parts in your inventory.

As for potions, every alchemist (and even rangers, when they get good at alchemy) can merge some potions. The simplest combination I can think of is a Light Heal + Moderate Heal = Major Heal.

*SPOILER*
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There are a couple of sites that come to mind with all of the alchemist's recipes and Gadgeteer's gadgets, look for some links in previous posts because I don't want to give it away, but One gadgeteer recipe I can't live without in the early game is Light Crossbow + Light Crossbow = Doubleshot Crossbow (35 Engineering req.)
and then Double Crossbow + Light Crossbow = Tripleshot crossbow (75 Engineering Req.)

The Alchemy recipes I posted to the Tips sticky thread just a couple of days ago. They include the Alchemy level needed to make each item as well as the three weapons that the Gadgeteer can make (as opposed to Gadgets they can make).

For the gadget list you can go to http://www.tk421.net/wizardry/wizardry.shtml and navigate down to his Wiz 8 Items page which lists every item found in the game and includes the gadgets separately along with what area you can find them in.