I'd agree with Mike: Try and keep the file as a 16-bit TIFF for as long as you can while editing, then convert it to a JPG for when you want to view it on the web. Also, some photo printing services don't accept TIFF files, you you may need to convert to a JPG for that.
To be honest, this is only worthwhile if you have many stages to your image editing. I use JPG most of the time, and it doesn't completely murder the image quality. But if I was ever to shoot pro, I'd definitely work with TIFF files.
One last thing: Be sure to delete all the "version 0.xx" versions of your image. TIFFs are big and can take up hard drive space very quickly.