I've been buying a bunch of the 20th Century Masters Greatest Hits or Best of collections .. usually at Walmart or Target for $5 ... sound quality is meh, but it fills in some holes, especially better known songs that weren't Top 40. Here's what's offered: 20th Century Masters The Millennium Collection
You can some on Amazon starting at $3.99 .. Amazon.com: 20th century masters - the millennium collection: CDs & Vinyl
I've picked up a few of these over the years they do fill the soft spots