What Size Screen ?  

A large sized monitor is always good. The main reasons are:-

You can end your works with less time than the typical small size monitor according to the results of a recently concluded research.

Also your eyes need to strain less since the words are bigger. Also the screen can be kept at a distance, decreasing the risk.

I am not saying that you should by 42 inch displays for that. But a 22inch will be good.

I don't think that changing and old screen is needed if it works well. I have a 14" screen. Possibly you might call it an antique piece. But I choose not to contribute to e-waste in order to save the environment. Most CRT monitors that are dumped are not recycled or reused by someone else. I don't support upgradation of computer peripherals as long as they are in working condition. I even have my obsolete hard disk in the computer cabinet that works for my backup.
I feel that upgrading peripherals implies wastage of money and pollution of the environment.

I think for laptop 15 inch screen is ok. For desktop the 17 inch is also good one. Even that would not strain your eyes. Plus if it does just increase the font size and use bigger icons. If budget allows go for 21 inch but i can not think of a bigger one.

I have a normal 17" LCD, not the wide screen version. Here in our place the prices of LCD are relatively cheap. The price difference between a 17" 19" is just a little. If you can afford you can go for a bigger one provided you have enough space where you want to put it. It's quite practical for everyday use actually. Take for example a 1280 X 1024 resolution will look bigger on a 19" or 22" compared to 17". Yes you can say it's OK if you just set it to 800X600 or 1024X768 & it would look bigger but you'll have less desktop space then

I have a 17inch monitor at home and a 14.1 inch laptop screen. I would recommend you to get a bigger screen if you can afford it. As bigger screens you can view your windows better and you can set it to different resolution and things look bigger and you don't have to strain your eyes so much. :)

I actually don't like big screens. I have a fifteen inch screen on my desktop, and I am currently looking to buy a laptop, which I plan on getting with no larger than a fifteen inch screen also. I feel that with a larger screen, your eyes have to move farther just to see something on opposite sides of the screen. I could see a large screen being useful if you were in the photo editing business or something like that, but for just everyday web browsing, I don't think there's any need to have a huge screen.

Currently I'm using a 22 inch wide screen LCD for my primary monitor and 19 inch widescreen for a secondary monitor. i don't always hook up a secondary monitor, but for me when/if doing any kind of programming or even just day to day work, it's nice to have the extra space to have 2 documents open and able to reference both easily without having to juggle windows.

The only real thing i'd watch out for is the gloss coating that alot of manufacturers put over their LCDs, the gloss coating is very reflective, and if the lighting in your computer room isn't right, it can make a great LCD look like trash. as i've said on other topics, make sure you do your research on anything for a computer that you intend on purchasing, many resellers put selective information on their products out there, and not all companies put the same info out there. Some stores do stoop to putting similiar sounding specs up that look better, ie Dynamic Contrast Ratio vs Native Contrast Ratio or any of the HD specs. Some of this stuff can be very confusing, and let's face it, sales people are under more pressure than ever to make sales happen. so do you're research better than ever, 'cause the sales person may or may not know what he's talking about!

i just bought an 19 in lcd montior from newegg.com i like it alot .........it is called an hanns-g it looks a lot bigger than a 19 inch

Go to the end of a corner of a window. You will see that the mouse pointer changes to a diagonal arrow pointing both ways. Now, with the left button of the mouse clicked, drag the arrow and resize the window to the desired size. If the problem still continues, open a few windows