Let's start with the original. No point in any elaboration on what is perfection.
Can't Help Falling in Love - Elvis Presley
A synth version would have been a total flop in the hands of anyone else, but when you have Vincent Clarke, the man who helped form Yazoo and Depeche Mode, it becomes something quite the opposite. (Do checkout the album Other People's Songs, that this is from; the cover of Solsbury Hill was rightly a very good one to gain such attention.)
Can't Help Falling in Love (cover) - Erasure
Now, unless you were deaf, you probably heard this next version in the 90s. Unfortunate that it was associated with the craptastic movie that it was, but, hey, the good news is it outlived that reputation very easily, since possibly only people who were given a free pass at the student center saw the movie (cough).
(It is a very good movie choice, though, for a Terrible Movie Marathon (tm me and V.)).
Can't Help Falling in Love (cover) - UB40
Usually, I don't like it when Bono gets all introspectively lovelorn on his songs; I much prefer him angry. For this cover, though, I think introspective and lovelorn with a hint of the anger beneath works just fine.
Can't Help Falling in Love (cover) - U2
Okay, we're almost at the top (i.e. the perfect cover, which by the way, I've mentioned before, so if you don't know what it is, you need to go back and read more!). Now, unlike Bono, I think Vedder does just beautifully on any song where he isn't angry, as great as that may typically sound. Maybe because he still carries his angst over, regardless of the tone. Seriously, the man's voice is just right. (Also, there is that lovely little minor chord again, right at the end, on the last 'take my hand'. When it's placed right, it's always golden, that little minor chord.)
Can't Help Falling in Love (cover) - Pearl Jam
And now for the piece de resistance. I've always felt this song should be sung more as a joyous anthem accompanied with giddy, happy out of your soul dancing, than a heartbreaking one, all tear stained and alone in a dark corner. Thankfully for us, someone else agreed with me, too.
Can't Help Falling in Love (cover) - Lick The Tins
(By the way, because I am evil, here is how not to do a cover of this song. Come on click, you know you want to. The video is worth the little bit of ear bleeding.)