"Legends In Concert" is always good entertainment ... at Imperial Palace around $25.
"American Superstars" at Stratosphere is another good one around $25.
"Jersey Boys" at Pallazzo is a bit more pricey at $60, but well worth it.
"Rat Pack" used to be at Greek Isles ... don't know if it's still there.
Beach Boys are at Buffalo Bills $38-$54
"Tribute to Neil Diamond" and "Sinatra and Barbara ... The Show That Never Was" at Riviera were excellent.
Sometimes 2-1 tix are available. Check the local magazines in town upon arrival. 50% off tickets can be obtained at "Tix4Tonight" or "AllAccessTickets" outlet (Circus Circus)