You should try jivosite.com live chat for you website. We offer 14 days free trial with many features. Free edition of up to 5 operators without time limits.
dude., i suggest live chat widget. this fits for e-commerce websites. I've read reviews for live chat software or widget . this may help you http://livechatreviews.org
Yahoo messenger is very nice, very helpful when I open a lot of other apps that I use at the same time with a unique look.
I use www.nerochat.com and it works great for me. Also the prices are affordable starting from $14. Recommend!
SKYPE is best for audio and video talk. I have been using it from almost 4 years. Don't have any complain with it till now. So my vote goes for Skype