I bought on ebay a year ago several wireless adapters with a large external antenna. Good range, recognized by wheezy and jessie Raspbian.
The lsusb command showed me those were RT5370 IC based Ralink devices, with driver support in the 3.x and 4.x kernel.

Witht he growing amount of Raspberry Pi’s here I thought it was a good idea to buy some more, and the Ebay adverts showed the identical looking device:

Mini 150Mbps 802.11N/G/B USB 2.0 WiFi Antenna Wireless Network LAN Card Adapter, about Euro 3

After several weeks they arrived, and the first test in the Windows PC’s showed a working wireless interface. So far so good.

In a Raspberry Pi alas, no WLAN0 device showed up. Time to troubleshoot!

lsusb showed there was a new USB device:

$ lsusb

Bus 001 Device 005: ID 148f:7601 Ralink Technology, Corp.

$ lsmod

<no device driver shown for this device>

The older working Ralink adapter had a different usb output:

$  lsusb

Bus 001 Device 006: ID 148f:5370 Ralink Technology, Corp. RT5370 Wireless Adapter

$ lsmod

rt2800usb 17716 0

So we have a new device, it is the MediaTek MT7601. Quick search with the ID 148F:7601 revealed this is indeed a new device. And it is supported with firmware in Linux kernel 4.2, the Raspbian kernel is still 4.1 and is not so far yet.

But a helpful post in the raspberrypi.org forums by MrEngman pointed me to the (now deprecated for kernel 4.2) to this command to load the driver:

$ sudo wget https://github.com/porjo/mt7601u/blob/master/src/mcu/bin/MT7601.bin -O /lib/firmware/mt7601u.bin

$ reboot

$ lsmod

..

mt7601u 73787 0

..

and all was well again.

Note this is tested on jessie

$ uname -a
Linux raspberrypwhplus 4.1.15-v7+ #830 SMP Tue Dec 15 17:02:45 GMT 2015 armv7l GNU/Linux

If you want to rebuild the driver, from the Mediatek driver source without debug info, follow this recipe.