I've lived in Las Vegas for the past couple years, and I must say that I am pretty impressed with most of what has been offered on here for must sees and dos in Vegas. All pretty good info.
Just a quick couple things...at the Barbary Coast Hotel and Casino (center of strip intersected by Flamingo St) you'll find the best deal on drinks at the bar. Only $2 for ANY DRINK. I drank more Crown Royal there than any man woman or child should ever have to admit too. (just kidding) Contrast that with prices of $12 a drink (call drinks) at many posh Vegas nightlcubs (the best ones in the country), and it's a steal. The Barbary Coast is a laid back, come as you are type of casino--with cheap drinks.
Best value Buffet in Vegas at the newly renovated Golden Nugget downtown. Good food on the cheap. I don't remember exactly but I believe it had pricing around lunch - dinner 9-12 dollars. Gourmet Buffett dining can be had at the All Suite Rio Hotel and Casino, and the Planet Hollywood (formerly Aladin). Those two are voted every year as the best in Vegas. Not cheap however, but incredible food.
It's true about what someone said above about the people in Vegas that are servicing you to some extent expect to be tipped. They are not there for their health. Even though those cocktail girls look to be in extremely good health.

When the poster above mentioned he tipped $2 a drink that is fairly common and just plain smart, you'll get great servide. You'll get phenominal service if you throw her a $20 for you and your friends and say keep the drinks coming, you won't have to tip her again and you'll have her undivided attention. The norm is 1-2 a drink. Just put yourself in their shoes ask yourself would you go out of your way to come back and service someone that was constantly stiffing you or would you work on those that were showing you a little appreciation? hmmm? Those cocktail girls, valet, bellman ect can't pay their rent with just a "thank you". Even though that is appreciated as well. Just not the ultimate thank you.
Here's one little nugget of info that I haven't seen on here. It's a nightspot called Ivan Kane's 40 Deuce. It's tucked away in the Mandalay Bay Hotel and Casino on the south west side of S. Las Vegas Blvd (the strip). It came from LA (and is still there as well). It's small, intimate cabaret lounge. At midnight and periodically after that, a female caberet dancer comes out and dances at a fast pace and is elevated behind the bar (to alive band on the side--elevated as well), she is a phenominal, sexy dancer. It's not a striptease, it's better with her skimpy clothes on if you can imagine that. She does 1 song and then disapears, it's kind of cool and she has the whole lounge standing (men and women) and starring with adoration.
My best steak dinner to date has been at N9NE Steakhouse in the Palms Hotel and Casino (main floor). It is a Chicago Style steakhouse and very cool. It's a dress to impress type of place though, with a menu to match. I brought my friend that has been around the world and he said it was one of his favorite places after I took him there. It has nothing to do with the $1000 hr hooker that sat down by us at the bar either.

The Palms has a lounge call the Ghostbar. It is on the to floor some 50 stories up. Part of it is inside and part of it is outside. It has stunning views of the strip. And a section of the floor outside is see through, so you can look down to the pool.
The best nightclubs are TAO (Venetian), PURE (Ceasars Place) and RAIN (Palms), and BODY ENGLISH (Hard Rock).
Best movie theatre is at the Red Rock Casino and Hotel, west of the strip towards Red Rock Canyon. It's a new property and just gorgeous.
Take a tour of Hoover Dam, it's a short drive and a lot of fun. It's an impressive structure and I learned a lot. Not only do you tour up above but you get to go down below in an elevator and stand above one of the pipes of flowing water, it rumbles and shakes the floor.
Best diner, in the Stratosphere Hotel and Casino, the name escapes me. But it's a 50's style diner and has great food. The waitresses/waiters get on the mic and sing as well. (Usually a good thing) Best Clubhouse sandwhich is in the Tropicana Hotel and Casino in their little diner by the giftshop.
For Mexican food on the strip, try La Salsa in the Luxor. And get the Margarita by the yard.
The MGM Casino and Hotel is extremely large and impressive. You've gotta check it out. Don't mind the live tigers.
NY NY Hotel and Casino is a great time, as mentioned by someone above. How can you go wrong with the ESPN ZONE?! The NY NY has a good, urban vibe about. Go to the storefront section on their and get your slice of pizza, it's great. The piano bar inside is a long of fun, he's a good entertainer (mixing it up with the crowd) and plays fun music.
If you like fine italian cars, check out the Wynne and it's lineup of vehicles.
The Wax Museum was ok, but you'll just have your partner taking pictures on a bed with Hugh Hefner and standing with Brad Pitt. You on the other hand will stand in the shadow of Superman Shaquile O'Neil.
Torrey Pines Pub is great on Griz gameday during the season, and the owner is a cool dude. A Real Griz fan. But I've never been their during the offseason. It's up in the northwest and my house is in the southwest (it's a half hour drive).
Someone mentioned In-N-Out Burger. THIS IS A MUST!!! It's just a couple Vegas blocks off of the strip (down Tropicana) and it is quite possible the door to heaven my friend. I'll leave it a that.