Are there any good intranet search engines?

Xapian Omega is amazing. And it runs on most operating systems.

From the website:

Xapian is a highly adaptable toolkit which allows developers to easily add advanced indexing and search facilities to their own applications. It supports the Probabilistic Information Retrieval model and also supports a rich set of boolean query operators.

Then combine this with Omega, again a quote from their site

Omega operates on a set of databases. Each database is created and updated separately using either omindex or scriptindex. You can search these databases (or any other Xapian database with suitable contents) via a web front-end provided by omega, a CGI application. A search can also be done over more than one database at once.

It is easy to install and get working and is very fast even on large collections of files. We use it to index a website upload directory and samba shares of ~350GB.

There's the google search appliance.. That should do what you're after... although it might cost you an arm, leg and kidney.. http://www.google.co.uk/enterprise/gsa/index.html