That was indeed the skinks, thank you. Wonder what the reason for parting with the skinks / moving them offshow was - they were nice animals and bred well.
Seconding what was said about the frogs and salamanders, although I would also add the Tokay Geckos to that list. For the frogs, your best bet is the long vertical crack along the wall to the left of the enclosure, but even this far from guarantees a sighting. For the salamanders, it is easy enough to predict where they will be (both individuals have a particular crack / hollow rock which they prefer, and friendly keepers stationed throughout the house should be able to direct you to the right one), but the problem is that these cracks are quite deep, so barring on the rare occasions when their head is right at the front, you will likely not see them. I have never seen them leave these cracks, nor have I heard any other member report this. For the geckos, try the very top of the enclosure.
Moving away from SloRA, other than the examples already mentioned, the gentle lemurs spring to mind. They were hard enough to see back in the Lemur House, but now they have been moved to the former spider monkey enclosure in Rainforest Life, I suspect they are even harder to see, as that enclosure is much bigger and does not have an onshow indoor area (for a mostly nocturnal / crepuscular animal, this is of course an issue). In the same building, the bokies never used to be an issue, but perhaps this is just my bad luck but it feels as though they have become much harder to see since the enclosure was renovated. Armadillos all but impossible, aye-ayes and pottos fairly likely but could require patience.
I see also that you mention you won't see the whole site, and I would like to say that you must not skip Blackburn Pavilion! Easily the zoo's best exhibit, and if your last exhibit was in 2007, then that would I believe be the year before its renovation / modernisation, so anticipate a lot of change. As far as rarities go, look out for both Scarlet-chested and Splendid Sunbirds as well as Collared Trogons and Ornate Lories, with Grosbeak Starlings and Javan Green Magpies in the outdoor aviaries.