I've been a user of freeconferencecall.com for years now, and I felt inspired to post here as a result of some awesome upgrades they've just put in place.
Most importantly, they now provide users with international dial-ins for several countries (click "View a current list of countries"). This means that you can host a conference call and provide an in-country dial-in to callers in the UK, Japan, Spain, Australia, and more.
The other recent service upgrade I've really enjoyed has been the change to access codes. Previously, freeconferencecall host codes were the same as guest access codes, with the * and # sign being the only thing to distinguish (ie 125899* and 125899#). Now, hosts and callers have different numbers entirely (ie 125899# and 943824#), making the service more secure and more professional.
Although I have access to other conference bridges at work, I'm not sure why I would use them. I've been embarrassed by double booking a conference bridge one too many times, and I simply don't worry about that issue when I have my own freeconferencecall dedicated line, free of charge... with international dial-ins for international callers!
Drop me a line with comments, thoughts, or suggestions about other services.
Also don't forget to follow me at @AdamStober on Twitter.