Diceware (http://world.std.com/~reinhold/diceware.html) is one version. It should be easy enough to automate, if you can get enough randomness to pick each word.

shuf -n4 /usr/share/dict/words

Maybe something like this? http://www4c.wolframalpha.com/input/?i=word-based+length+32+...

http://passphra.se does exactly that =) Although it's sadly not https.

True, but there are two reasons for that! One is because I'm too cheap to pay the premium my web host demands for https. The other is because most of the entropy is calculated in your browser via Javascript (even borrowing a JS implementation of SHA-1). It's extremely unlikely that either I (the server), or a third party sniffing packets, could guess the passphrase you generated using passphra.se.