Actually, it's "worth" whatever the company paid you to build it. Well, I mean, thats what its worth is to them.
And, if once you made it - if it then brought in new revenue and clients that before that the company didn't have, well, sure there's an equation for that, but its significance would only be for the company itself. I mean, only another company doing exactly what its doing could ever desire it.
Namepopper.com rank: www.xtlonline.com 4 (very low)
Alexa: 1,318,046 (not great)
xlt isn't a common combo and the domain xtlonline is 2 words w/ an unfamiliar acronym. (not good)
So the domain itself value is pretty low.
The site design is nice for a straight forward corporate page, nice flash animation and basic info.
So.... Outside of the company that it's for, i hate to say it has little value