Please keep in mind that laws change, and if you want the most up to date information you should visit the "Official" sites before the others, as the others may not be updated as regularly or accurately. Please post if you have other useful sites to recommend.
Official Sites:United States Citizenship and Immigration Services
http://uscis.gov/US Embassy in London
http://www.usembassy.org.uk/cons_web/visa/iv/ivindex.htmEmbassy's Site on Application Times
http://www.usembassy.org.uk/cons_web/ins/i130filing.htmForms from the Embassy's Website
http://www.usembassy.org.uk/cons_web/visa/forms/visaforms.htmOfficial Poverty Guidelines (for the Affidavit of Support I-864)
http://travel.state.gov/povert.htmlNon-Official Sites:A helpful forum created by a UKY member who has made the move:
http://forum.diveintoamerica.com/index.phpA lawyer's US website that is chock full of information and FAQs about visa processes, including FAQs about the Affidavits of Support and other subjects.
http://www.immigration.com/A site for people immigrating to the US from all over, including UK to US. Very helpful forum, and also has forms and loads of other information.
http://www.visajourney.com/This is a forum of expats, and includes at the bottom some Usenet Groups that can be massively helpful, such as alt.visa.us.marriage-based, etc.
http://britishexpats.com/forumI-130 Immigration Help Site.
http://www.geocities.com/immigration_helpsite/I-130/index.htmA page of personal stories, UK to US, including K1 (fiancee) visas and I-130 processes.
http://www.k1homepages.com/#ukThorough general information guide to newcomers to the United States.
http://www.newcomersguideusa.com/Abbreviations:•ADIT - Alien Documentation, Identification & Telecommunications System
•AOS - Adjustment of Status
•AOS - Affidavit of Support (you have to do this after you marry)
•BCIS - Bureau of Citizenship and Immigration Services
•CPR - Conditional Permanent Resident
•CSC - California Service Center
•DCF = Direct Consular Filing
•DOJ - Department of Justice. BCIS (INS) falls under the jurisdiction of the DOJ
•EAD - Employment Authorization Document
•FAQ - Frequently Asked Questions
•IBIS - Interagency Border Inspection System
•INA - Immigration and Nationality Act
•INS - Immigration and Naturalization Service
•IRS - Internal Revenue Service
•IVACS - Immigrant Visa Applicant Control System
•NG - Newsgroup
•NOA1 = Notice of Action 1 which you get to confirm Immigration has your visa application
•NOA2 = Notice of Action 2 you receive this when the I-129F for example has been approved
•NVC = National Visa Center
•PISS - Pre-INS Submission Syndrome
•POE - Port of Entry. Usually airport or border crossing inspection post.
•PR - Permanent Resident (Also LPR - Legal Permanent Resident)
•RFE = request for evidence
•SSA - Social Security Administration
•SSN - Social Security Number
•TPS - Temporary Protected Status
•USC = US Citizen
•USCIS - US Citizenship and Immigration Services
•VWPP - Visa Waiver Pilot Program