As for me -- while Iogear's product is not the cheapest of the three listed above (at a list price of US$99.95), I was so impressed with the demo version that I went out and bought my own online for US$70.
Smaller than the proverbial pack of cards, the Iogear nevertheless does a flicker-free job of powering my Dell CRT at 1280 x 1024 resolution and 32-bit color. Watching YouTube videos or DVD movies is rarely a problem, either. The only hiccups I encounter are ones I can also find on a single-screen setup, such as when I've got half-a-dozen apps open or the ThinkPad's fan is running full blast.
Iogear also offers a digital DVI version for large LCD monitors that can support up to 1600 x 1200 resolution. It lists for US$149.99.
Cost for Iogear External USB Video Card: US$70 (street)
Step 3: Take control of your monitors
Most of the video adapters you choose will come with their own window management software. For example, DisplayLink Manager, which ships with the Iogear and many others, is competent at adjusting the settings of your various windows, and even has some rudimentary shortcuts.
But power users looking for more features will want to look elsewhere.
Realtime Soft's UltraMon, the creme de la creme of multimonitor software, has two unique features: the ability to set hot keys for common commands and the ability to "remember" how big and where you like your application windows to open. UltraMon also lets you easily move windows from screen to screen, adjusting to changes in dimension, e.g., from a wide-screen monitor to a conventional 4:3 one.
UltraMon also lets you create different wallpapers and screensavers for each monitor. For power users, this US$40 Swiss-made Windows utility is worth every penny. Note: It's compatible with most video adapters with the glaring exception of the Matrox Dual/TripleHead2Go products.
MediaChance's free MultiMonitor task bar is for users who don't want to pay US$40 and mainly want the ability to quickly send app windows from one monitor to the next.
DisplayFusion, from Binary Fortress, claims to offer nearly all of UltraMon's features, apart from letting users preset how and where app windows open. It does allow users to search for and download images from Flickr for wallpaper purposes. DisplayFusion costs US$10 for the full version and requires Microsoft's .Net Framework 2.0.
Cost: US$40 for UltraMon, US$10 or free for other utilities