I would suggest you to go for WHMCS.
Take a look at AWBS and ModernBill as well.

We have actually switched from ClientExec to WHMCS. THey have great support and there software is really easy to use and integrate.

You can get WHMCS licences for around $100 from licencepal

I would suggest ClientExec if you are looking for something cheaper or for a little bit more you could go for WHMCS which is my key recommendation.

i have awbs, looks great even hardly to customize

i reccomend whmcs is it what we use. it suites us pretty well,

I would have to say your best bet is WHMCS. I use it and it gets everything done quick and easy. Unlike modernbill its not slow and not confusing at some parts

WHMCS is becomming / if not already the industry standard now.

I am still going to have to recommend ModernBill, even though I do not agree with the buyout by Parallels. It is great software if you do not need support. Otherwise you are hooped.

I used to have Modernbill as a billing system, I musta say that it is very inconvenient and has many unnecessary features.

I agree with you guys,that WHMCs is much better

By the way, do you know where to get cheap licenses for WHMCS?

I recommend WHMCS...

There seems to be a lot of support for WHMCS and I also support WHMCS. Very easy to use, absolutely fantastic for hosting. It makes things much easier if you don't have to manually set up every single account. It automatically sends Paypal invoices, too =D.