MY SUGGESTED CARTOS FOR THE EGO:
(other opinions will vary on this topic, these are simply what I have had the best luck with)
You need to be looking for the 510 Boge cartos, silver threads, around 3.0 ohms. (regular cartos) (These are typically used on devices that go higher than 3.7 volts.)
REGULAR CARTOS
And for the LR cartos go for the LR 510 Boge cartos around 2.0 ohms (LR cartos).
(carto of choice if using on a standard eGo battery)
LR CARTOS
Check any of the suggested retailers on the forum here and find what you need. Vapor Talk store has some regular cartos in stock... but I don't think he has any LR cartos right now.
(I much prefer the LR cartos if I'm vaping at 3.7 on the eGo. This seems to be the carto of choice at this time for many people.)
One little word of advice... once you have filled them with whatever method you want... I would suggest putting the "condoms" back on and letting them sit for 30 minutes or so. This will let the juice get good and soaked in like it needs. And remember, once you do start using a carto, it's always smart to keep topping it off every hour or so to keep them good and wet.
And most importantly... if you can at all manage, you should use PG based juices in cartos to get the best vaping experience possible. VG based juices are simply too thick for most of them to wick well enough to keep up with most of us. There are a small handful of folks that don't have any issues... but for the majority of people VG is just a real hassle. Hopefully you have some PG based stuff you can fill them with so you don't get bummed out when you can only get 2 or 3 good drags before the flavor/vapor is drastically diminished. :