Some interesting search engines

A couple of weeks ago I posted about a way to get more results from your search engines (i.e. beyond the number of maximal results for a query). I then referred to Ask Jeeves, which has been along for quite some time, and provides a nice query refinement interface.
I was asked whether I know of any more search engines, which provide more features than the features available by the 3 giants (Google/Yahoo!/Live). Well, here's my personal list (in no particular order):

A9 - Simultaneously runs your search on various data sources. For example, you can enter a query and it will search for images, books, web and wikipedia all at once. The results are then presented, all on one page, but in a separate columns for each data source.
Vivisimo - Clustering of query results into groups of related results.
iBoogie - Clustering of query results into groups of related results.
Mooter - Clustering of query results into groups of related results. The clusters are presented in a graphical form, and when you drill-down you get a similar tree-like interface like the others.
DogPile - Simultaneously searches all major search engines (Google, Yahoo!, MSN, Ask Jeeves and more). The results are presented in aggregated form, with an indication of which engines returned it.
KartOO - Clustering of query results into groups of related results. The clusters are presented in a graphical form. Their UI may seem somewhat complex, but it's pretty cool once you get used to it.
WiseNut - Groups related results into categories. It generates much less categories than other similar engines.
Infonetware - Clustering of query results into groups of related results.

If you have anything to add, please let me know :-)