A more light-hearted swamp adventure might be the ticket. Old Man Katan and the Mushroom Band (Dungeon #41). After Old Man, I might transition away from the swamp as the adventures can be overly claustrophobic if multiple swamp adventures are run sequentially.
I might instead select something newer: Demonspore. You'd be supporting small press authors working now, as opposed to a 35 year old published work. In addition, it's one of the best supplement produced in recent years. Here's a review: http://tenfootpole.org/ironspike/?p=645
So they're up against the alt-cult that broke away from the mainly-evil reptile cult?
Another old-school option that more or less sticks with the general lizardy theme would be the three U-series modules. You might need to stick something in between N1 and U1 however, if they come out of N1 still all at 1st level.
Lan-"now I want to alt-name some other classic modules"-efan
I was planning on running Quagmire after that module.
My version had come about because of an attempt to swap the kingdom with its double in the Shadowfell.
Although the ritual was thwarted it did weaken the dimensional boundaries enough for certain evil gods to penetrate that world releasing servants.
In the above scenario it released a Naga and its spawn with the spawn possessing locals thus allowing for them to take over the local church.
In the game I ran the cleric player eventually used a figurine of wondrous power that summoned a Lantern Archon who upon understanding the situation cat called the deity that church belonged to and that deity collapsed the hidden temple beneath the church causing what few members of the evil cult to flee with whatever Naga Spawn remained.
The same event that released the Naga and its spawn would also be the reason behind the city from Quagmire collapsing into the sea and a call for aid requiring the PCs to decide on whether to make the trek to the port city on foot (0r horseback) or by sea if they can find a seaworthy enough vessel.
Not that hard since they start at a fishing village.
Sorry for the longwinded explanation, but what events led to you running Against the Cult of the Reptile God?