I don't use photoshop at all, I use aperture (light room would work exactly as well) and I batch them.
Or lacking the expensive software, you can batch resize and re-name with Irfanview. (FREE!
http://www.irfanview.com ) Generally I don't go over 800 x ??? for web pages, because that will display the image large enough for a nice view, without spilling over the sides, or making the browser re-size it. Most of the time for a gallery the thumbs are 120 or 140 wide, which makes it so I can put five across. Many times I dumb down the photos to 640 wide.
Also I save at 80% on Irfanview, just because they look nice and it reduces the size. Just a number I picked out of the air, no science.
Believe it or not, some people are still dialup or have slower internet. Fast loading web pages are more viewer friendly.
Here's a nice one. It's OPG which is OnePageGallery, not to be confused with another site that makes a One Page Gallery

This one is a simple php code that finds the pictures and makes the page. I mean REALLY simple. You only need to have a directory of photos and within that directory another folder named TN which holds the ThumbNails. As long as the names are in the same sequence, the thumbs and images will match.
Main pages is a block of thumbs with a black background. When you click on any one of them, it opens the larger image.
It has right click defeated, but that's easy to get around. It's just a nice inconvenience. People who right click get a message saying, email <your name> for more information. (or whatever you code into it)
It makes multiple pages with Index 1 - 2 Etc. When you are viewing photos it has a Previous - Next arrow. All automated, no more coding necessary.
If you don't do HTML it's easy, and ready to run. The Index has documentation, and things like <page title> and clear instructions. Of course I whomped it up a bit on my pages and added a Buy Photos link, email link and counter, but, as issued, it's just fine! Oh and once again FREE!
http://www.onepagegallery.com/
And should someone want to see what a one page gallery looks like. Here's one I whipped up in minutes, last Summer.
http://www.gizex.com/gallery/sports_car_road_america_2007/