For light stuff I use Notepad++, but for serious XML work Altova's XMLSpy is the heavy hitter.
A unique feature I like is the ability to graphically display the structure of xml schema (really handy when developing to a particular XML file type), and their Gridview gives a nice graphical display of raw xml data too.
If you do enough XML work to justify the purchase price, I'd highly recommend XMLSpy, although it's hardly a steal at €399 currently.

You might look at Steve Gibson's Spinrite, from grc.com, although its not free, so I'd go for one of the other programs mentioned.

Personally I use VolumeTray, an excellent little program that sits in your Taskbar.
It provides two options for changing volume:
1.   Custombisable hotkeys
2.   Left click on the taskbar icon = volume up
     Right click on the taksbar icon = volume down

By default it puts two icons on the taskbar, which is a bit of overkill, but it can be very easily customised in user preferences to use just one.

Grab it from http://glorysoft.omsk.ru/