It's been awhile since I've talked about image editing tools. My favorite website for quick and easy editing (cropping, resizing, etc) is still Pixenate, but I recently read about Clipping Magic - and it is amazingly awesome.
Here's how it works: upload your image, draw a green line through the part of the photo you want to keep, draw a red line through the background you want to remove, and you're done:
The live preview on the right lets you adjust your lines to get as close as possible to what you want - and since you can change your line size and zoom in on the image, you can really fine-tune it.
I've been using Photoshop for years to do exactly this, and this is way quicker. Photoshop is still better of course, but like Pixenate and other web-based tools, I have access to this no matter where I am in the library (Photoshop is only installed on the computer on my desk in the office, which I rarely actually use).
Unfortunately, it looks like Clipping Magic is only free while it's in development. Hopefully it'll stay that way, but try it out while you can.