Gold pieces are the standard currency of NWN2.
Gold pieces do not have weight. "Gold coins are weightless because the minting process involves mashing up little air mephits to create a weightless alloy. Because this alloy is only possible with gold and not copper or silver, copper and silver currency has fallen out of favor and hardly anyone uses them anymore, certainly not adventurers. In short, a wizard did it." 
- Obsidian has indicated that currency will work much the same as it did in NWN, i.e., hardcoded gold pieces.