I have heard the anthem “Be still, my soul” (which is sung to the tune from Sibelius’s “Finlandia”) sung in Finnish by the Helsinki University choir. At least I assume it was “Be still…” since I don’t speak two words of Finnish - but whether it was, or whether it was a laundry list set to music, it was gorgeous.
Italian
Scots Gaelic is lovely to listen to.
I also like Finnish, and Brazilian Portuguese (and find Brazilian Portuguese to be much nicer than Portuguese Portuguese).
Russian is beautiful. I particularly like the /S/ and /Z/ sounds.Verdurian, a conlang created by Mark Rosenfelder, is also very beautiful (probably because it sounds a lot like Russian).
I also really like Quenya and Spanish.
Spoken German and Hebrew sound very cool, but for a different reason. They’re a lot harsher, with lots of back fricatives, rounded front vowels and uvular /R/. I really like that phonology, but I wouldn’t call it beautiful the same way Russian or Quenya is.
I think French is ugly as sin (all those ugly nasalized vowels-ugh!), and I don’t understand why people find it beautiful or romantic.
[hijack]
A German, a Frenchman, a Spaniard, and an Englishman are walking through a meadow arguing about the relative merits of their respective languages. A butterfly flies past them, and the Englishman says, “Gentlemen, see: here is a wonderful example of the expressiveness of English. The word ‘butterfly’; does it not capture the way this creature moves through the air?”. The Frenchman replies, “Ah, but in French, the word ‘papillon’ almost perfectly expresses the delicate nature of the animal.” The Spaniard says “These are fine words, no doubt, but gentlemen, consider ‘mariposa’: this beautiful word is, you must concede, nearly a perfect match for the beauty of the creature.” There’s a pause, and they all turn to look at the German, who says, “Und so vas ist wrong mit ‘Schmetterling’?”
[/hijack]
That;s funny! I think you have to be either German or a linguist to like that joke. 
Russian, of course. But I’m biased, because that’s my major.
Close runners up are:
-Greek. It’s much prettier than its main competition, Latin; it just flows much better.
-Coptic. It’s all vowels and softness, plus it has the feel of all those great Egyptian names you learned in school.
-Lao. I once knew a Lao girl, and could have listened to her talk in this language forever. Even yelling matches between her and her mother sounded pleasant.
Ditto for Anthony Hopkins (also from the same area as Burton).
I’m Brazilian so my opinion might seem biased… yet I still find Brazilian portuguese quite nice to listen too and too speak… if the accent isn’t too heavy.
I don’t know if written language counts… but I think English is the best language for written sagas and stories. The choice of words and constructions are great.
hmm…i’m partial to… Klingon…no wait, that’s not right
maybe it was Sebecean, naah, that’s just backwards English…
Elvish, yeah, Elvish that’s it, no wait, it’s a nonexistent language
okay, of the real languages, i’d have to say Japanese
Italian!
I find it interesting that so many people here are putting Spanish down as beautiful. I personally have always detested the language. I find Portuguese (especially Brazilian <nods to Rashak>) to be much more pleasant. I guess I just love sibilants and diphthongs. Vowels! Give me more vowels!
French is good in that respect, as well, but Italian is not. Despite being of Italian descent myself, I’ve never liked the language that much.
Hey, schmetterling is perfect. It sounds just like you’ve just chewed up and spit out a butterfly.
Once you speak Portuguese… Spanish seems like it lacks certain sounds. Sound wise its more simple than Portuguese. It might have the romantic connotations… but it still sounds stunted to me.
Well, Brazilian Portuguese is perfect for that. Even something simple like “Eu não sei” (“I don’t know”) contains three dipthongs and only two consonants. And the most beautiful Brazilian word “saudade” contains one dipthong, two other vowels, a sibilant, and just one lousy normal consonant!
Actually, I came in here to say English. English is my love.
But other than that, secondary would be Japanese.
You might want to try the Hindi/Urdu programmes on BBC’s Asian Network –
link
I will add that in my opinion, whilst Urdu is the beautifullest language, the Scottish accent is very very sexy.
Ancient Greek. Liquid, beautiful, and a sublime philosophical vocabulary. I could have listened to my ex-bf read his Greek exercises aloud for ages. And sweet-talk. “Συ φιλώ…”
French, Spanish, Italian–all the romance languages. Gorgeous!
As a singer, I enjoy singing in Latin. Once you learn the pronounciation, it is easy, and it sounds very nice. German, on the other hand, is a royal bitch to get right. But, when you get a full chorus singing a major German work, and they ALL get the pronounciation right, it sounds like nothing else on earth (“Jauchzet, Frohlocket”)!
Otherwise, I am not a very big fan of singing either French or Spanish, although both sound lovely spoken. I have sung in Russian (Mussorgsky) - the lyric was spelled out phonetically – difficult and interesting to hear. I have also sung a number of short folk songs in Hebrew.
Hands down, though, the most difficult language I have ever sung was Swedish. With most of the languages I have sung in, even if you don’t know the language, the various phonemes are more or less familar, and, more importantly, occur in various parts of the phrase with some sort of order that is, to an English speaker, more or less predictible. Swedish might as well have been Martian!