My loadout is Needle Shot, Toxic Atomiser (UV: High vs Slimes) and a Graviton Bomb. It serves me well, mostly. My Toxic Atomiser is normally all I need for slimes.
I've started to encounter Toxilargos (http://wiki.spiralknights.com/Lichen#Toxigels) in danger rooms and such, and they kick my ass. Getting close enough to damage with the toxic is dangerous, Graviton doesn't neutralise them as a threat the way I'm used to. Never seen a Sloombargo, and at least poison will work on them, but I don't think I'll fair too much better.
I'm trying to think of better ways to fight them. Is Nitronome good against them? How do you all fight them without getting pinned to a wall by spikes? Do I need to suck it up and carry a Pepperbox? I like Needle Shots and would rather not shelve mine, and you can't always anticipate when you'll fight these things.
Any -largo Slime needs to be zoned.
Freeze is the best way to do this.
They are pretty much impossible to fight up close so Cryotech Alchemers are the easiest way to stop their gas spreading.
Freezing Vaporizers are good, but for the most part, you will find yourself suffering at the lack of damage.