Recommendations for a Softphone to use on a local PC or remote laptop?

I did a few searches looking for this, but get way too many hits and don't seem to have luck narrowing it down.

I downloaded X-Lite, and it was easy to configure it for basic testing, but it seems very limited now that I am getting into more advanced functions. Also, the features such as transfer, etc, require purchase.

I also haven't seen a lot of people tallking about setting up soft buttons, and the "hard" buttons don't seem to be programmable.

So, what do you recommend for a soft phone for a local PC, and/or a laptop that will connect over the internet to the phone server? How much does it cost? What features are available "for free" vs the ones you get when you pay for it?

Please post as much info as you want about your favorite softphone.