One of the good sources to do searches today have been released with the name of Clusty ?!?
He one of the better SE in clustering today, specially with broad subject or for clustering the live of a friend with the exception of the mode cluster ;-)
The major problem I found is to get fresh results. Clusty is using the SE databases of; GigaBlast, MSN, Lycos, Looksmart, Wisenut, Open Directory and Overture. All of thoses take weeks, if not months, to get new sites in theirs index compare to Yahoo and Google.