I will be adding to these sites as I make new discoveries, please feel free to add suggestions in the comments.
Community:
http://www.expatforum.com/expats/america-expat-forum-expats-living-america/
Immigration:
http://travel.state.gov/content/visas/english/immigrate/immigrant-process.html
http://blog.mygcvisa.com/2013/09/nvc-consular-processing-steps.html
Certification:
Police Check: https://www.acro.police.uk/police_certificates.aspx
Health records: http://www.nhs.uk/chq/Pages/1309.aspx?CategoryID=68&SubCategoryID=160
Copy birth, marriage and divorce certificates: https://www.gov.uk/order-copy-birth-death-marriage-certificate#before-you-start
Pensions in the UK:
National Insurance: https://www.gov.uk/new-state-pension/your-national-insurance-record-and-your-state-pension
Housing in the USA:
Healthcare in the USA: