My favorite tank to use with the iStick 50W is the Aspire Triton 2. I have seven of them, four in rotation. They also have a mini version but I like the bigger tanks (about the size of a regular Pro Tank 3) because I don't have to fill them as often. There are smaller box mods out there, I prefer having the longer battery life of the 4400 mAh size. If you figure how long your Spinner 2s last at 1600 mAh, think how much longer a 4400 mAh battery would last.
Right now, on one of my iStick 50W, I have a Kanger Pro Tank 3 on it with a 1.8 ohm coil and it works just fine at 8.0W of power. These days I now prefer to use by wattage instead of volts that I was used to with the Spinners. I've also used Kanger Pro Tank 3 minis with the eGo adapter on it with no problems.
I get the wraps from ebay. Although I never recommend buying hardware from eBay, I have no problem with wraps as they're just little things that wrap around the battery. Nearly all of my iStick 50W are black with different colored wraps on them. Mightyskinsdecals1 is the vendor I use.
http://www.ebay.com/sch/i.html?_odkw=iStick+50W+wraps+skins&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR3.TRC2.A0.H0.XiStick+50W+skins.TRS0&_nkw=iStick+50W+skins&_sacat=0
There's the link for the search. You can scroll through to find what you like. Just keep in mind that once you put the wrap on, you can't really just take it off and change it without stretching the wrap, they're only good for one time use.
As for the battery, I've purchased nearly all of mine from MyVaporStore at $34.95 each. I've gotten great customer service and their price for the 50W is about the lowest I've found.
The second from the right has the Kanger Pro Tank 3 on it.