If you didn't notice yet, there's a new, seemingly unimpressive, nevertheless very useful, extension on the horizon, namely ext/hash.
The initial version, proposed by Sara and Stefan -and it seems that Rasmus had his hands on it too- already featured the most common algorithms, and it has recently been extended to support now fairly every algo which libmhash provides.
There's not been any public release yet, which means you'd need to build from CVS. pecl4win though, already provides fresh modules for Windows users.
It's usage is simple and intuitive
Hashing a string:
echo hash('sha384', 'The quick brown fox jumps over the lazy dog');
Hashing a file:
echo hash_file('md5', 'release-1.0.tgz');
There's also an incremental interface available.
The recently released version of the HTTP extension now uses the HASH extension instead of libmhash for generating its etag hashes.
Just in case you missed, Sara released pecl/hash today.
Check it out -- It'll be bundled with PHP-5.1.2!