My personal records for least humans in the raid. If a number isn't given I did it myself.

Ony25 (3, my 10, kobalt 10, stealthy 5)
Ony10
VoA10 Toravon/Koralon
Uld10 FL/Ignis/Razor
OS10
OS25 (5, my 10+4 singles, drakes done with 3)
Naxx10 Spider/Plague/Patch (2-3 for the rest sans KT)

A long time ago some zerg people did naxx25 but I don't remember our specific accomplishments. We did several bosses with 3-4, got a few soloers in for some more.

I know naxx10 was full cleared before I got in there, I know at least one person did each of the voa bosses before me, probably more. I'm sure os10 was done before me too. I know FL was done before but I'm not sure how far into uld was cleared.

I'm unaware of anyone who did ony10 before me, or anyone who came close to 3-man ony 25. os25 with less than 5 is easily doable but I'm unaware if it's been done.

Marrowgar is going down soon(tm). I'm sure I can down him, it's just a matter of me not raiding with my raiding guild during the week and getting into icc with more than 40 minutes to maintenance. I hope to head into toc10 soon, and I'll be hitting up Malygos, XT, and more bosses in naxx10/uld when they become the weekly or I'm bored.

Feel free to add in your own accomplishments, but lets avoid the "I 4-boxed with 21 other players" type. The goal here is least amount of humans, regardless of how the characters are divided. As a rule of thumb if you have more non-boxers than boxers it probably doesn't belong here but there can be exceptions, like my os25. Even if it's not a record breaker go ahead and brag about it. Feel free to share your failures as well if you've attempted something like this.