http://licensepal.com/products/zopim.php 7.45 a month is a nice deal

Zopim is excellent. LivePerson is another solid choice albeit significantly more expensive.

Is there any FREE one that can offer 1 operator only ?

there are many free chat solutions

www.volusion.co.uk
www.comm100.com/livechat/
www.chat4support.com/

are just 3 off the top of my head

My vote goes to Zopim, remote chat service provider donot use your web hosting server resources to have chat system working as well as very affordable pricing and fast chat system.

We use Crafty syntax so far it has met our needs. Plus it has a Iphone app which seems to work pretty well.

Live Zilla used to be great untill they decided to charge large amounts for there services , I would personaly recomend livehelp.stardevelop.com they have a real good system which also links in with whcms.

yes i moved from livezilla to the WHMCS livechat (stardevelop). only downfall i find is the ability for clients etc. to upload images to the livechat

We use Kayako but unless you brought into it with V3 I think V4 is a bit expensive.

Actually looking to upgrade to V4 next month so we can provide a bit more a review