It does not exist today. There are products such as those you have mentioned which have tried, but in my experience none of them will make an experienced Excel user happy.
My company makes Excel compatible spreadsheet components for use with Windows Forms and ASP.NET. We have been getting this question for years, so we have of course considered building one because it looks like a good business. But HTML / JavaScript is just not a suitable platform for building something which "feels right" to users who want it to work like Excel - IMO.
We have settled on the idea of building a spreadsheet control for Silverlight. I believe this will give you the best of both worlds - cross platform rich interactive spreadsheet in the browser which any Excel user would be comfortable with. Unfortunately, that is not going to happen this month or next...
At my previous company, we actually built a spreadsheet component as a Netscape Plugin, as an ActiveX control and as a Java Applet. They had a little bit of success, but none of these technologies ever became ubiquitous in the enterprise for various reasons. I believe Microsoft is finally getting it right with Silverlight and that Silverlight will become the gold standard for browser based Line of Business applications in the Enterprise.
EDIT:
I should have mentioned that the product I alluded to above is Formula One / NET (Netscape Plugin released ~1995), Formula One / ActiveX and Formula One for Java - which is now sold by Actuate as e.Spreadsheet. I left in 2002, but AFAIK they still maintain the Java Applet which is probably the best example of an Excel like UI in the browser (I have no interest in the product any more - in fact we compete to some extent with e.Spreadsheet and intend to have a better answer with a Silverlight control in the future). I did not mention it by name in my original answer because it is a Java product - not a .NET product - but it is a potential answer even for an ASP.NET web site.
Lloyd Cotten correctly comments that Google Docs is an example of a spreadsheet built with HTML / JavaScript. Lloyd says Google Docs "definitely 'feels right' in its similarity to Excel". While I respect Lloyd's opinion, in my experience Google Docs does not 'feel right'. Perhaps this is because I'm a spreadsheet guy. I do know that we talk to potential customers almost every day who are trying to solve the problem of the OP, and they have all looked and cannot find one they are happy with - but of course they would not be calling us if they had so we are dealing with a biased sample and I understand that.
So I just want to clarify that there are in fact plenty of examples of HTML / JavaScript grids and spreadsheets which are usable. It's just that I don't want to have to use them because I expect certain keys to do certain things and a particular level of responsiveness which is just not there today with any of the HTML / JavaScript solutions I have tried (and I look at them regularly because my company could definitely sell such a product if it were feasible to build one that we could be proud of).