When I really got into genealogy, I went for the census records soon as I had the names of a couple and the general area.
http://www.censuslinks.com – you can find census records on here for both UK and also Ireland, there are also links on this site to some other amazing census records.
http://www.censusfinder.com – lists many links to free census records, in particular for the UK.
http://census-online.com/ – lots more links to census records on this site also
Immigration records are another of the best things to search for if you find your ancestors came from overseas, which is the case for many of us.
http://www.irishrootsmagazine.com – information and advice when searching records for ancestors from Ireland.
http://www.genuki.org.uk/big/Emigration.html – emigration and immigration records for UK and Ireland, also with links to lists from America, Asia and Oceania.