FocusWriter is my favourite program in which to write poetry. I tried the free version of OmmWriter, but disliked that I couldn't modify it, so was stuck with a wintry background and limited music. So I started using FocusWriter, for which there are downloadable alternative backgrounds, many of them. I also have a folder of New Age mp3's which I downloaded (copyright free). At the beginning of a session, I randomly select about 15mins of music, put Windows Media Player on repeat and play the selection with the WMP volume low. This plays the music quietly while allowing me to hear the keystroke sounds.
For anything in prose, I use Write or Die. Absolutely LOVE the program. I've used it for NaNo, first drafts (I copy and paste into Word's Outline view at body text level), and to ensure that I write something every day. I use a small app called MikkoMatrix for prompts.
These, Word, and a free program called Papel - great for planning - are my absolute faves. I've trialled Scrivener, WriteWay, and many others, but always return to these.