I'm writing this because I've noticed, off and on through various threads, that a lot of people tend to get stuck in designing pages based on what they see when making pages. The setup I have now makes it very easy for me to see what a much broader section of the web audience is seeing, and its changed the way I build pages.
What you need, ideally:
3 monitors - At least one should be LCD, and at least one should be a large monitor (19" LCD or 20-21" CRT).
A graphics card (or cards) that allow multiple monitors to be running simultaneously with different resolution settings.
How they should be setup:
The large monitor should be set to a high resolution - 1280x1024 or higher. This will be your "production" monitor.
The two smaller monitors (17" typically) should be set to the two most common resolutions, being 1024x768 and 800x600 respectively.
My setup: (not bragging, this is just what I have and works well for me.)
A 19" LCD set to 1280x1024. Two 17" CRTs (one perfectly flat, the other an old style curved front). The perfectly flat is set to 1024x768, the curved is set to 800x600.
Why you should try this out:
When working on a new layout/design, it becomes very easy to get "lost" in the screen space that you're working with. A lot of us have fairly high end machines with large, high resolution monitors. It's very easy to forget that this simply isn't the majority of the web surfing audience. Fully 30-40% of machines surfing the web have their resolution set to 800x600, because (as far as I can tell) a lot of people out there find it easier to read text when their monitors are set to this resolution.
However, if you have three monitors on the go, with all three resolution settings mentioned above, it's very easy to have a browser window open in each monitor, with the page you're working on displayed on all three. Whenever you make a change, you just have to save the file and refresh the view in all three windows.
This gives you an immediate sense of how the page is going to look for different segments of your audience. You would be surprised how small changes can bring important graphics/text above or below the fold on various resolutions. You will also be surprised at how easy it is to generate a layout that forces the infamous "side-to-side" scrolling to be able to view an entire page.
Also, it will give you a better impression on how graphics (which tend to be fixed size in terms of pixels) can become more and less dominant on a page, simply by changing screen resolution.
Text that is legible at a lower resolution, can sometimes become minuscule and nearly illegible on a higher resolution monitor (and NEVER assume that the end user knows how to resize text - most people don't know this, and even if they do, they tend to be too lazy to bother).
Conversely, text that is at a nice, legible size on a high resolution monitor can become overbearingly large on a lower resolution monitor.
Why the mix of LCD and CRT screens?
Graphics and colors display very differently between the two types of monitors. LCDs tend to be crisper, which is good for text, but also harsher when displaying gradients, which can have brutal results when looking at an over-optimized JPEGs.
CRTs, on the other hand, tend to blend out JPEG artifacts, giving you more room for optimizing images, but at the same time, you lose crispness, so small text tends to be somewhat harder to read.
Overall, the mix of resolutions and monitor types is hard to visualize unless you're actually looking at it. With experience, you learn that certain types of layouts and certain color choices are bound to cause you grief.
But even hard won experience is nothing compared to actually putting your eyes on the screen.