There are 2 very easy places to see plenty of reps
One is East Head right in Darwin itself
Plenty of monitors and various slitherers in the bush etc etc
Other one is the Springs at Humpty Doo also very close to Darwin
Plenty of File snakes and Golden Tree Snakes and some huge barramundi to hand feed
Loads of Frillies on the road up to the Vernon islands boat ramp
Lichfield can be great but its the end of the dry season so water will be low and not too much around generally
Get up into the top gorges at Katherine and pretty nice country
Sorry mate, dont know how long since you've been in the Top End but here's a bit of an update.
Havent seen a varanid at East Point since the toads got established. Or a frilly or blue tongue for that matter. Still a pretty place but the Monsoon Forest is much better in the Wet. It's dry and bare at the moment.
I think the springs you are talking about are the Howard Springs (Nature Park.) The springs have lost a lot of their flow due to agricultural and domestic bores depleting the aquifer. You cant swim there anymore and the big barra are gone. Also Parks "remodelled it" and knocked out a lot of the big overhanging trees. Not currently reccommended.
The road to the Vernons I think is the Gunn Point Rd and there some fabulous camp sites if you know where to go. Same story, frilles & goannas rare. You're going to get that anywhere in the Top End at the moment.
Litchfield is worth a look but if you prefer a more isolated experience the same formation outcrops 100km away and you can have the same thing without the crowds.
For herping (and birding for those who twitch) I would reccommend the southern end of Kakadu and the country between there and Pine Creek. Big range of habitats, escarpment, open woodlands, riverine forest, etc. Koolpin Gorge is especially reccommended but you need a permit from Parks (as with any overnight walk in Kakadu) and numbers are limited so hop on soon. The whole region is really good (and underated).
If you want crocs do an overnighter on a houseboat on Coroboree Billabong (Mary River). It's food for the soul....and the fishing's not bad if you're so inclined.
If you want Indigenous art sites then Injulak Hill at Gunbalanya (Western Arnhem Land) is unforgettable. Again you would need to arrange it through Injaluk Arts (I think). In advance.
Anyway pm me with your wish list and I'll give you some advice. I can lend you maps when you get here, I have most areas covered.
Peter, I'll send some photos soon and thanks again for sharing your snakes.