Spending other people's money? Us? Never!
Tam recommended a couple of great items with the iStick 50W and the Aspire Triton2 (which I have the V1 and V2, and use both), and I'll make a few additions myself, of workhorses that I use daily/weekly... without suggesting anything too advanced...
For a basic tank, I love the Kanger Aerotank V2. It has a decent capacity and great airflow... and they're very inexpensive! There are also LOTS of different coil resistances available for them, from 0.5 Ohm, all the way to 2.4 Ohm. I personally prefer 1.2 and 1.5 Ohm in them.
For an intermediate tank, I cannot recommend the Kanger SubTank Mini highly enough. Great airflow, good flavor from the coils, and they look good too, lol. I would suggest the horizontal coils over the vertical coils though, as they last longer and taste better, IMO. There are also many resistance options available in the coils (as well as an RBA deck for custom building)... AND, in a pinch, the Aerotank coils WILL FIT and WORK.
For box mods... the only integrated battery mods I use currently are the Wismec Presa 40W. They're light and small (portable like your eGo's), have an all-day battery built-in, and fully adjustable Wattage control. They even offer a TC version for $5 more, and a 75W TC version for the same price... but it requires an 18650 cell, but can also charge that cell via USB (like the 40W versions, or your eGo).
For replaceable cell mods... those that take an 18650 battery... I love my Cloupor Mini and Mini-plus mods... they are small, durable, and work very well. The plus version offers 50W and TC, where the standard is only 30W, but more than enough power for most vapers. They also have lots of cool colors, and the paint doesn't fade/chip nearly as bad as many of the others.
Pioneer 4 You (IPV) makes great mods, too, and I love their IPV minis, although they are getting harder to find. 30W for the V1, 70W for the V2, and they feel great in your hand, and have a bit of heft to them.
The Kangertech 50W mod that also comes as a kit paired with a SubTank mini is a great little mod, only slightly larger than the Cloupor Minis, and my only complaint on them is that you can't lock the buttons so it's very easy to accidentally adjust the wattage up or down without knowing it. The 75W TC kit comes with the new Top-Tank (top-fill subtank), and I've not tried them yet, but my SO has a top-fill Nano, which works well, and doesn't leak. Which also brings me to the Subvod kit... a 1300mAh large eGo style, non-variable, with a subtank Nano (smaller capacity subtank). I don't really like the non-variable battery, but they do make great backups on a budget.
If you go with a mod that requires an 18650 battery, do yourself a favor and purchase quality, genuine cells... and I recommend the Samsung 25R5 (green) as the best all-around vaping battery, and they are also the most inexpensive, too.
Well, there's my best-of...