I've published a series of short stories through Amazon and I find their service to be very good. Quite straight forward to set up and get started. Smashwords[0] are also supposed to be quite good. They have similar terms to Amazon and will spread your book to other sites such as Apple, Kobobo[1] and a few others.
Things you may not have thought about:
1. Get a good quality cover image, pay for one if you have to,
2. Write an interesting and compelling blurb,
3. Have other people read your work before you publish, if you can afford to hire an editor.
1 and 2 are the first introduction to your book so need to catch the eye of the potential reader. 3 is vital, especially in longer works, as you will miss things.
What's the book about?
Oh and good luck!