If you upload to Flickr a lot (as I do) the Flickr export plug-in for iPhoto is a godsend. Highly recommended.

You can find a number of Flickr-approved uploading tools by heading over to http://www.flickr.com/tools/ There’s a plugin for iPhoto that you can use to send your images directly from iPhoto to Flickr, but it costs £12. Since I’m a cheapo, I just use the Flickr Uploadr tool that’s available directly from Flickr - you simply drag the images you want to upload from the iPhoto window over to the Uploadr window, and once you’ve selecting all the images you want to upload, you can tag them individually or in batches, create new photo sets, add titles and descriptions, and then upload them all with the press of one button.