To get started, the best video lessons for me was Cynthia Lin's mini ukelele lesson series. Cynthia Lin is an awesome teacher and starts from the absolute basics of playing the uke and singing along.
To push playing beyond just strumming and learning songs, RockClass 101 with Andrew Hardel has to be the best I have come across. His lessons have a stronger technical focus, and are mostly via songs he arranges for ukelele. Some free video lessons while for a very affordable membership fee, you can access even more songs, tabs with music sheets, and an online play-along tool.