I usually start out with 1000 px width in my Photoshop designs. However, if you haven't heard about it yet, "responsive designs" are the future (or so I'm told). That means you don't design for a specific resolution.
They are called responsive because they change with the width of the browser using CSS3 media queries (so that it will look good on any resolution, and those using iPhones, iPads, etc. do not have to zoom). You should definitely look into it. For example, try resizing the window on this website: http://forefathersgroup.com/
If I do design for fixed width I use 1000px width.
1000px is indeed a good starting point! And its a pretty versatile width for designing! as for responsive designs it is indeed a really good way of making sure that your website is displayed properly on numerous resolutions! However i find that it is pretty tricky to code and implement