io questa frase la direi "Cos'è l'amore?"

o anche "Che cos'è l'amore?"

@Guybrush88: Actually, I adopted this sentence, which wasn't owned by anyone (in order to capitalize it).

Can it still exist, side by side with the variant that you have just offered (which I'm also familiar with), or do we have to change it?

well, the original sentence sounds quite strange to me, but it can still exist in that form, since its grammar isn't wrong

Maybe we can add a suitable tag, to qualify it. If you have any idea, let me know and I'll add it.

I'd say something like "unnatural", but I don't know xD

:)
Should we ask Pharamp? :)

maybe it's better if we ask her xD

Ok, I'll send her a message.

So.
"Che" + "cosa" is good, but "cosa" + è is always "cos'è".

If you put "cosa + è", you put a great, great emphasis on what love IS (so on the è). But it can be only a rhetoric sentence from I don't know... a priest or in some shows... and also, it's just the "importance" of the word "love" that makes this sentence possible in a very few few few cases.
Then, it would be something like "Che cosa è, l'amore?" or "Ma che cosa è, l'amore?" (both incorrect translations).

But "cosa è" is completely unnatural in everyday usage. You cannot render an emphasis such as this one while writing, and it's not correct Italian a "cosa è" without an apostrophe, in both spoken or written register.
I've found a YouTube video http://www.youtube.com/watch?v=1iO5ze_l0sA where in the title there's a "cosA è", but it is surely an error, nobody would speak like that in this particular case. In fact, when the girl repeats the sentence, she says "cos'è".

I suggest to change it to "Che cos'è l'amore?", and then I will think something else. Guybrush88, do you agree on what I said?

p.s. I add that anyway "cosa" + "è" + a past participle (cosa è stato, cosa è accaduto, cosa è successo) is completely acceptable. I don't know the reason, but really "cosa è" sounds terribly.

Grazie mille.