Google

http://www.google.co.uk/addurl.html

Yahoo

http://submit.search.yahoo.com/free/request

DMOZ

http://www.dmoz.org/help/submit.html

MSN Search

http://search.msn.co.uk/docs/submit.aspx?FORM=WSDD2

Mirago

http://www.mirago.co.uk/regions/submit.asp

AOL

http://search.aol.co.uk/web_idx?help=add_sites

Alexa

http://pages.alexa.com/help/webmasters/index.html