I knew the David Cassidy one  I also knew a good few of them were covers. Just not who by 

Didn't know most of those EC, was surprised!

Without You - Nilsson (Badfinger original)

Yes, I knew that one 

Oh yes, I'd forgotten about that one Joe 

Essentially Taurus by Spirit with a couple of added banjo licks and some lyrics!

Ah! That old chestnut! I do like Spirit's vershum of All along the watchtower mind.

ION I think Jethro Tull have a better call for t'eagles ripping them off for Hotel California.

I did know the Ray of Light (Madonna) one.

This was actually quite well known at the time. The original was a very different arrangement, and Kim Carnes' success was often cited as a classic example of the importance of getting a good producer/arranger (Carnes' first, demo version was also very different to the finished product).

As for "Denis": at the risk of annoying a certain other FM, I have to say that every time I heard the Blondie version, it always sounded to me like Debbie Harry was singing "Denise, Denise..." - the original lyrics...

Bloomin' One Show nicked my post and ran a very similar article tonight. They featured some on the list and added a couple of others.

One could say I was ahead of the curve.

Maybe they've been spying on you?

Aha, so you're admitting it now. *taps nose knowingly*

Darn! what am I saying!!!

That's the cover blown.

 I didn't watch all those episodes of Spooks without picking up a few hints and tips.

Nothing Compares to You by Sinead O'connor was written by Prince and was first used on an album by a Prince-affiliated act named The Family.

Prince wrote "Manic Monday" for the female trio that he created; Apollonia 6... but lost interest in the project and it was later recorded by, and a massive hit for The Bangles.