I adore all of his shows, not just "Lost in Space". Thanks to the genius of Hulu, many of them are available for easy consumption: Lost in Space (I watched early on Saturday AM), Land of the Giants (this scared the heck out of me as a kid), Voyage to the Bottom of the Sea (watched with my grandfather on early cable), and the Time Tunnel (which I only recently finished watching...these didn't seem to get much re-run time in the 70's). He had two other TV shows, but I do not remember them well (Swiss Family Robinson, Code Red).
Hulu has many of them available through this link. Settle down for a cheesy treat!