I was, I admit, a little stubborn when starting development on the web interface about using php. I still think there are advantages in terms of widespread knowledge of php, but I'm quickly coming around to the point of view that it is overkill.
Possible languages as I see it are
Ash - the advantage is this is already built in, the disadvantage is that there is a little bit of a round peg square hole issue since, of course, it is a shell scripting language. Not impossible, just possibly inefficient.
PHP - the advantages as I see it are universallity and a wide range of functions to use/backport in. the disadvantage is size and the truth is -- as i've been coding the interface -- you don't really need very many functions to write a web interface, especially as you can tie in to shell tools for many things
Ember - this looks to be ideal. i'm hardly the first to suggest it. my concern initially was that its not so widely known. my current thinking is that (a) i may be wrong about that, (b) regardless, the syntax is so easy that anyone knowing c/java/php could pick it up in about 8 seconds, (c) its size makes it worth it. (full disclosure: i'm casting my vote for ember)
HTML - i guess it would be possible to write the entire thing in HTML. of course there would have to be hooks to cgi (c progs or shell scripts). the big problem here is that it would be no fun. who wants to rewrite html code all day, when we have scripting languages.
I am merely summarizing things others have already said before. But, hey, let's put it to a vote.
I won't swear I'll rewrite my interface in the winning language (I'm still a little stubborn ), but I'm definitely looking to move away from php.