King Solomon's Mines is an awesome read. I've been trying to get my hands on the sequel.
As a kid, The Cairo Jim Chronicles series used to fill the void of Indy. There's also the spin-off Jocelyn Osgood Jaunts series, a Marion Ravenwood like character, who was a flight attendant who got too curious and who's Cairo Jim's "special friend."
What's been filling the void lately? The Young Bond series. Yes, the series based on James Bond, 007. He has one Indy like adventure (the 4th book, Hurricane Gold), complete with a boobytrap filled labyrinth!
Even the comic books of The Phantom are very Indy-like (I personally love the film as well, which involves crystal skulls of their own!).
Also, again, kiddy, The Story of the Amulet by E. Nesbit. Still worth the read though.