I'm a big Move/ELO/Wood/Lynne fan. There are a lot of great songs across all the ELO albums, but the style or approach or whatever you want to call it changed over the years. The first three albums (Roy Wood is on the first one) sound different from the middle albums, which are what people usually think of for ELO. I like both eras, but the more well-known ones might be an easier place to start, if someone's looking that.
Out of the Blue has a lot of the big hits that people would know - Turn To Stone, Sweet Talking Woman, Mr. Blue Sky - though it does have some songs I could do without, like Jungle and Across the Border. A New World Record has a lot of the ones people would be familiar with, too: Telephone Line, the remake of Do Ya, Livin' Thing...Shangri-La on there is great.
El Dorado is probably my favorite ELO album.