For relative newbies who end up using Photoshop, I recommend you learn to use the nifty "unsharp mask" function (before "saving for web") - you'll find it in the "filters" menu. The name "unsharp" is misleading - it's effect is actually to SHARPEN UP images that have been downsized. The feature has a "preview" window and three sliders, and takes a little bit of finesse to use - but it can work like magic to bring low resolution images into sharp focus.

Another counter-intuitive thing about downsizing jpegs for web use in Photoshop is it helps a bit to check the box for progressive display. (You've probably noticed some web images first appear blurry as they load and then come into focus... for some reason those images are smaller than images that display all at once.)

Photoshop is a very powerful tool with way more features than most people need... but I still recommend it. Have fun!