From my understanding lembing generally have a shorter shaft, and meant to be thrown while tombak have a longer shaft and use for closer combat. The note from malaysian wikipedia mention that tombak generally has a wider blade. But as long as I understand nowdays people just call it tombak and never lembing
As for tombak, probably one of the most popular is Tombak Kyai Pleret (google should give more than enough information on this)
It classified as wesi aji, the precious steel.
But any cutting knife (and steel in general) seems to be "precious" in the past, at least it still celebrated in Bali (Tumpak Landep ceremony).
Attached is photo from KITLV website but I forget the caption. It shows many fighter with tombak in the background.