Of course, disco songs do come to mind. If the theme is funky, I'd suggest "Car Wash"; if the slide show is long, I'd go with the long cut of "Disco Inferno" from the Saturday Night Fever soundtrack.
Or, maybe a medley of songs as you go through the decade. Maybe a little "American Woman" to start out with a nice hard riff with a good melody; "Me and Bobby McGee" because you can't do the 70's without Janis; then maybe a little from the theme from "Shaft"; play on the angst of the early decade with a little "Miss American Pie" and then "Tie a Yellow Ribbon"; then "Hooked on a Feeling" by Blue Swede (just because of the ooga-chaka); "Cats in the Cradle" by Harry Chapin (I love his music); then, another love song with "He Don't Love You Like I Love You" by Tony Orlando & Dawn (that's 2 by them isn't it, but I always liked that song); and because it was the disco decade, "Jive Talkin'" by the BeeGees, and then the trucker's favorite "Convoy" (I remember watching that guy do that song on American Bandstand with a CB mike in his hand

); "Silly Love Songs" by McCartney and Wings; then, "Disco Duck" by Rick Dees followed by "Stayin' Alive" of course; "Dreams" by Fleetwood Mac; the theme from "Star Wars"; "Grease" by Frankie Valli; "Miss You" by the Stones; "What A Fool Believes" by the Doobie Brothers and finally "Hotel California".
Human government bears the same relation to hell as the church bears to heaven. (David Lipscomb, On Civil Government, 72).