I don't know what your budget is, I can't recommend a specific laser but I can tell you where to buy parts to build one. I built mine myself from parts, but I can tell you that even only 82mW has a visible beam in dim lighting, but I guess if you want something impressive you will want a bit more power than that. Try this one in the 200 - 300mW range: SF501B 520nm Forest Green
That one would be built with the PLP520-B1 diode instead of the weaker PL520 that I am using.
That is $370.99 for the 1W+ version but the beam will be about as impressive as you can get in a hand held battery powered laser. If you pointed it at the international space station (don't do that) they would be able to see it if they were looking out the window.