Went back in March of this year for the 1st time (honeymoon) & we had an absolute blast! We stayed at the Monte Carlo it's a little older but GREAT room rates, CLEAN & a nice central location on the strip and it's next door to the super luxury Bellagio.
Do a little online hunting before booking a room, you can get some VERY reasonable room rates through the casio's websites & most will beat the rates that get posted on the search services like Expedia or Orbitz.
Things the wife & I have been recommending to people:
The buffet at Paris, the food was absolutely incredible!
Freemont Street, they've done a great job restoring some of the "original" casinos, JUMBO frozen drinks in a plastic football

, some cool cheapo souvenier shops (gotta get some goofy tourist crap right?!) & the light show on the huge overhead canopy (covers an entire city block) is worth seeing.
Aquarium at Mandalay Bay has a VERY cool sunken ship room & is very well done overall (compareable to somethig at Seaworld IMO)
Excalibur , this is one of the oldest casinos on the strip but was fun, has a big breakfast buffet that is pretty darn cheap & the dinner theatre / knight's tourney was a hoot.
Car display at the Imperial Palace
Buffet at the Rio, it's an off-strip casino & VERY tacky theme here but MAN the buffet there is HUGE & pretty dang good for the money.
I'm probably forgetting a ton of stuff but hopefully this helps a bit
Doug C.