On the gateway servers
( http://www.umich.edu/ )
we have chosen to use the Google University search service:
It is free, they do not include advertisements, you can create your own
account and set up a google University search customized for your web
site, and we've found the service to be nothing short of fantastic.
The one real limitation with this service is that you have no control
over when or how frequently your site is re-crawled for changes. They
index approximately every 25 - 30 days. If this is not often enough
for your needs you may wish to look at our swishgate program:
This is the search software in use, for example, on the ~jobs site:
which really shows off the degree of customization that is possible.
Please let us know if you have any further questions.