I've been using 8x8 for a while now and I'm very happy with their service. There are plans for home and business. Here's all the details on their website.

I have been using Blueface and find them great, for me the call quality is better than Skype.
http://www.blueface.ie/

Source: http://www.blueface.ie/

I use PhonePower -- Can't beat their 2-year $200 deal, and you get a "cloned" line (i.e. you can plug in another phone, and it acts just like a second line)

We decided to try MagicJack. At $40 for the 1st year and $20 per year after that, we figured it was worth the experiment. So far we've been very happy with it, with the exception of the fact that it can't connect to some free conference calling services (but that's another story).It's got pretty nice features, like emailing your voice mail to you as attachments. I also love the fact that you can take it with you wherever you go and your phone number goes with you.It's not suitable for a small office that needs to transfer calls internally, but for solo professionals I think it's a viable option.I'm also getting ready to experiment with a combination of Gizmo5 and Google Voice that I read about on Lifehacker.