1. "It's So Easy Falling", by Manfred Mann.
Listen (from the 2.07 mark) here; or download here.
(The YouTube clip linked to above compiles two Manfred Mann songs, with "It's So Easy Falling" appearing second. They are both worth a listen; if you thought that Manfred Mann's career started and ended with "Blinded By The Light" (and oh how I love that electric piano), you might be pleasantly surprised.)
2. "After Hours", by Caribou.
It is no secret that Caribou's particular skill lies in crafting songs (which are frequently excellent in their own right) using bits of other people's songs. But until I stumbled upon the first few seconds of "It's So Easy Falling", from Manfred Mann's "Mighty Garvey!" album (from 1968), I had never had a clear example of him actually doing it. (It may be that his sources are almost uniformly obscure; or I may be a not particularly good listener.)
And while we are on the subject, I recently had the opportunity, courtesy of our local library (your taxes at work), to finally listen to Isaac Hayes's "Black Moses" album. (He was much more than the voice of Chef.) Therein lay a surprise, even if I am the last to have discovered it. It goes like this.
First, refamiliarise yourself with Portishead's "Glory Box":
Then, listen to "Ike's Rap II":
See how easy this is?
If it is true that all the good songs have already been written, then I suppose you might as well use them as building blocks for your own songs. (But query what is going to happen in a few years' time when the songs that are based on other songs are themselves used as the basis for other songs. My head hurts.)