the Star Trek thing is pretty cool. the Speed roller coaster at the Sahara is worth a spin, as is the Big Shot on top of the Stratosphere (the coaster is lame though). get a cab though, they're a hike from the Monte Carlo. the coaster at New York New York isn't bad, just don't sit in the back or you're in for a rough ride. the motion rides at Excalibur and the Luxor aren't that great, but the Luxor has a good arcade (as does NYNY). the elevator ride to the top of the Eiffel Tower at Paris ain't worth 9 bucks. the park behind MGM Grand has a couple of cool rides. the Circus Circus indoor coaster isn't bad, but that hotel is generally loaded with screaming children and people whose first language is not English.
the EFX show at MGM (featuring Rick Springfield!!) is also worth seeing, definitely more than most of the other shows i've seen in Vegas. Mystere is pretty decent. all the shows have an inherent cheese factor though, so fair warning