I often need to send photos via email, and because it's good practice and good manners not to block up the recipients inbox with very large photos (ie. leaving the photos the default size that the camera creates) I always used to use Adobe Photoshop to optimise them to a manageable file size. Recently, I started using Microsoft Windows XP's built in "Send to >> Mail recipient" which you can find by right clicking on the image(s) you want to send and choosing "Send to", and then "Mail recipient" from the menu, but found it to be a real pain and incredibly buggy, even though it was much easier than optimising in photoshop. So I decided to find out what other options existed to perform this simple function.
I was looking for something that was both free, good quality, and easy to use, and found Google's Picasa and Adobe Photoshop Album Starter Edition v 3.0. After trying both, I have settled on Picasa - the photoshop album has an irritating register screen that appears every time it opens, and also causes the photoshop downloader to appear in my sytem tray (and I can't get rid of it). Although both could send to email very easily, Picasa seemed less intrusive. People have complained about the picasa.ini files that it creates in your image folders (used to store any edits you've done - originals are left untouched), but these are easy to remove once you've uninstalled: just search your system for all "Picasa.ini" files and delete them.
I haven't had time to use many of it's features, but tried the redeye reduction feature and was blown away with how easy it is to use - just drag over each redeye and it removes the red. All in all, I'm very happy with Picasa, and sending photos via email is no longer a mission.