AltDesk virtual desktop manager from AstonShell is a small application I downloaded for free as Giveaway of the day. At work I use two monitors – the laptop’s and the 24″ Dell, which generally doesn’t require any additional desktop management, but at home I frequently have two switch between the contexts of home (Firefox, e-book reader application) and work (Outlook, WinSCP, text editor, IRC). So AltDesk comes in pretty handy, as it allows to drag the active windows to the separate virtual desktops, and then switch between those desktops.
The regular price for the app is $15, and depending on how cluttered your desktop your usually is, it might be worth it. Drawbacks: you cannot launch multiple copies of applications for the apps that don’t support multiple copies (text editor, Firefox, etc.), and music players play music regardless of which virtual desktop you’re in. But overall, a pretty useful productivity tool.
I have recently developed a similar need, and I’m using this open-source application: VirtualWin, http://virtuawin.sourceforge.net/
It allows me to create up to nine virtual desktops and assign different settings to them (depends on the plugins you choose to use). It has a small memory footprint, and perhaps you should give it a try.