Fragrant Heart I put this first, because it is probably the site I use most, maybe because of the huge variety of topics addressed. From meditations of just a couple of minutes to some over 15 minutes, there is something for every mood and schedule. Elisabeth Blaikie, who writes and narrates these meditations must put an enormous effort into this project. She has a soft, gentle delivery with just a slight New Zealand accent. There is a great Learn how to meditate in five days course, which you can follow on the website at any time, or subscribe, and have it emailed to you. It's not very demanding, but it will help you get started toward the more "empty mind" style of meditation quite painlessly. I also love her Guided Visualisations of the Tarot series. "The Tree" and "Blue Sky" are two more I really like.
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Philip Carr-Gomm is the chief of the Order of Bards, Ovates and Druids (OBOD) as well as a trained psychologist. I put this second because he hasn't produced a great deal, and generally you have to buy his recordings. That said, I find his guided meditations among the best I have ever experienced. Perhaps the best. Luckily, I happen to know a few secret places where you can find some of them to listen to for free. Both "A Meditation with all Four Elements" and the wonderfully awesome "Clothed With Flowers" are on this page (scroll down a little when you get there). I can't recommend them highly enough! Philip speaks with an English accent that should be easy for non-British folk to understand.
The Meditation Podcast also has a great archive of guided meditations with excellent music. Jesse Stern, the narrator, has a beautiful speaking voice and a quite neutral US accent. These podcasts are free on the website and on iTunes. Two of my favourites are "Releasing Fear" and one of the best meditations I've heard: "Positive Thoughts". Jesse also has some meditation music CDs for sale on the website.