You can use any Ego or 510 cartomizers though very low ohms ones may be a bit risky (like down at 1.5 ohm - some will only go that low w/ a mod and some will use 1.5 on Ego) and anything above 3.2 ohm would be too cool
You can use any non-tank Ego or 510 atomizers with the same ohms caveats. An Ego atomizer can use an Ego drip tip and a 510 one can use a 510 drip tip which is handy for testing juices etc. You can also use the appropriate cartridges on those atomizers (not the best way to vape but may be handy for an extended test of a juice or vaping one that is thicker than cartos like)
And there are some big handmade carto tanks like MAP, ARY, Torpedo, Stormy's and other BIG carto tanks with replaceable carto guts that I have never tried.