I've got a programming device called USB AVR JTAG-ISP v. 1.2.
Where can I find drivers and a good IDE for it?
For Windows, AVR Studio 4 as per the other answer.
For Linux, you want the avr-gcc and AVRDUDE packages from your OS distribution, plus your choice of C IDEs for Linux.
For OS X, you want Crosspack and Xcode.
On Linux or OS X, depending on which device you are programming, you may need to download the source for AVRDUDE and rebuild it, which will require that you also get libusb 0.1.12 (not libusb 1.x).
I find AVR studio to be infuriating, buggy and generally terrible.
Eclipse (available on all platforms) has wonderful end-to-end AVR integration available if you install the avr plugin, avr-gcc and avrdude.
If you're running on Ubuntu beware that it doesn't always identify the ISP right off the bat