First off, everyone NEEDS the 3 disc Roger box set King of the Road - The Genius of Roger Miller, especially discs 2& 3 - amazing stuff!! There are a few unreleased songs from albums that were lost (Treat Me Like A Human, What Are Those Things...). I can't explain how good that stuff is. Roger literally became my favorite singer/songwriter of all time after listening through the box set (competing with my favorites Waylon, Wille, Johnny, Bobby Bare, Merle, Elvis and Alice Cooper). Roger went right to the top of the list.
I'd also recommend the Best of Roger Miller IMPORT - 30 songs, most alternative versions. Buddy Killen told me he didn't like this CD because Roger was out of it and not into it, and you can hear it. They aren't quite as good as the original but they are really enjoyable plus there are a few songs on there that I haven't seen released previously. Great Value, worth getting after the box set.
If you don't have it, you need to hunt down "Uncle Harvey's Plane" - amazing track, there are 2 versions released from the studio, one you could tell Roger was on another world when he cut it, awesome. I do that song at most of my shows and people really seem to enjoy it, in fact, much more than the material I write :( It wasn't written by Roger but he made it his own.
There was a Readers' Digest CD set released a few years ago, lots of really good material, the only place I can find it occassionally is on Ebay. That's one worth picking up.
I haven't had much problems ordering online. So I would recommend getting that BEAR Family one (ebay is probably the cheapest but check amazon), they did a really nice biography written up in there and released many of songs that are awesome that didn't appear on the box set. There's easily enough solid material for there to be a second box set.
There's another "greatest hits" CD released I'm told with the same 10 or 12 songs from every other greatest hits CD but this one comes with a DVD with just interview clips. I haven't seen it yet but I hope to soon, I'm told it's good.
FYI, Ebay is a pretty safe place to buy from IF you buy from someone who has a high rating and quite a few sales (I'd say anything over 50 with a score of 95% or higher is worth buying from).
It's killing me, but I have a deadline to meet by in the morning, so I'll have to come back tomorrow. I don't think they would understand how I was hanging out here. ;-) Thanks for your comments. I'll be back when I can breathe.