Here are some benchmarks for genealogy sites as of 30 September 2012. Comparable figures a month ago are shown in brackets. The higher the Alexa ranking the more popular the site.
Findmypast.com has jumped in Alexa rank this month.
Familysearch.org has 1,302 (1,233) record collections: census & lists 118 (114); birth, marriage, & death 813 (779); probate & court 106 (99); military 98 (96); migration & naturalization 66 (58); other 101 (87). It has Alexa rank 4,207 (3,993).
Ancestry.com has Alexa rank of 624 (642); ancestry.co.uk ranks 7,485 (7,972) and ancestry.ca ranks 27,631 (26,585). There are 30,892 (30,773) datasets in the collections including 1,932 (1,932) for Canada, 1,318 (1,236) for the UK and, 24,992 (24,980) for the USA.
Findmypast.co.uk has an Alexa rank of 21,136 (21,929). Findmypast.com ranks 70,120 (110,236).
Family Tree DNA has 392,433 (389,801) records in its database. It ranks 37,071 (36,112) on Alexa.
Mocavo.com has rank 45,172 (47,037); GenealogyinTime.com ranks 29,999 (29,042).
Britishnewspaperarchive.co.uk claims 5,741,158 (5,614,605) pages digitized. Alexa rank 131,346 (127,752).
Cyndislist.com claims 323,109 (320,365) total links in 190 (190) categories, with 1,904 (2,931) uncategorized. Alexa rank 79,160 (82,137) .
FreeBMD has 220,463,424 (219,464,977) distinct records, Alexa rank 66.368 (71,635).
UKBMD provides 2,367 (2,328) links to web sites that offer on-line transcriptions of UK births, marriages, deaths and censuses. Alexa rank 219,988 (217,982).
CanadianHeadstones.com has over 486,000 (464,000) gravestone photo records from across Canada. It scores 406,163 (336,363) in Alexa traffic rank.
bifhsgo.ca ranks 731,412 (721,198), qfhs.ca ranks 3,756,174 (3,750,908), and ogs.on.ca ranks 205,273 (214,174).
And in case you're curious: Anglo-Celtic Connections has 3,944 (3,868) posts and has fallen back a bit in Alexa rank to 209,954 (203,779).
Did I miss something significant? If so please post a comment with statistics.