Well, how about African fat tail geckos? They're probably the best bet, for something you can put in the same rack as leopard geckos. Very similar care needs, they just need it a bit more humid and not quite as hot. They get a bit bigger, have a slightly different look, and, at least from what I've seen, are often more laid-back than Leopard geckos.
That's about all I can think of, though. Everything else has drastically different care requirements (i.e. crested geckos--too cool and arboreal to share a rack with leos), or are snakes...
Though there might be a couple, less common species of gecko that are close enough to leopard geckos to share the rack... Might find a good gecko forum and ask for suggestions there.