SQL Group By question

I have a simply query where I'm trying to pull the most recent record from my table grouped by a certain field but I'm having a bit of brain freeze today so hopefully someone will be able to show me where I'm going wrong:

There will be times where the accountid will have multiple opportunityid records but I only want the most recent one (the new_applicationdate).

Here is the code I have atm:

SELECT     TOP (100) PERCENT accountid, accountidname, MAX(new_applicationdate) AS [Latest Application Date], new_producttype, opportunityid
FROM         dbo.FilteredOpportunity
GROUP BY accountid, accountidname, new_producttype, opportunityid
HAVING      (MAX(new_applicationdate) IS NOT NULL) AND (new_producttype IN (1, 2, 3, 4, 5)) AND (accountid = '40B98E4E-FAE1-E111-A6E2-00155D101911')
ORDER BY accountidname

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I have 5 columns I'm pulling back from:

accountid; accountidname; [Latest Application Date]; new_producttype; opportunityid

What is happening right now is I am getting all the opportunityid records coming back for the accountid and I'm only after the most recent one.

I'm aware I could change the code to SELECT TOP(1)... but this will not work as I'm merely filtering on the accountid for testing and this will be removed so it will be looking at a table with thousands of rows in it.

Hope that makes sense and any advice appreciated as always.