I've had two wanting-to-shout moments while researching my family. They both occurred at an FHL research center, while looking at microfilm.
The first was the marriage record in Iowa for my great-great grandparents. Hurray! Hurray!
The second was this one: Finding that our family name change was documented not just once, but twice. How lucky can a researcher get?
In the village of Llanafan, during the time of patronymics, our family surname was - for a while anyway - Jones. Then when the law was created to provide consistent surnames, ours became Richards. Which is a good thing, as there are a one or two fewer Richards families than there are Jones families.
Document 1:
Bontfach, Baptisms, Llanafan Y Trawscoed Parish Registers, Source: FHL film 0105150
No 271, Aug 6 1837, David son of John and Jane Richard / Jones of Bontfach, Labourer, baptism performed by J P Morgan, C[urate] of Rhostie. No 271 Note [in beautifully clear handwriting - at least on the film!] "Richard altered into Jones in the original register book. Richard was entered by mistake owing to John Jones' brother David (number 267 above) going by the surname of Richard. by me D E Jones August 13, 1837"
Document 2:
---GRO, Entry of Marriage, 1838, Qtr J, Vol 27, p 25, Cardiganshire, Wales, Anne Richards to Joseph Hughes
"Anne Richards, of full age, spinster, res Bontfach, father John Richards alias Jones, labourer."
David, in the baptism record is my great-great grandfather; Anne in the marriage record is my great-great aunt.
Whoopee!