Alternative to Excel as ASP.Net Report Generator

I use excel through vb.net/asp.net to generate reports from a web page and then send the file down to the user. We've had some issues with Excel being super slow/inefficient/not closing (even when we keep track of the process id and try to kill it in code...). So I'm looking for some flexible alternatives. We need a replacement that can:

Allow for inidivdual cell formatting including borders (different settings on each side), background colors, font styles/coloring, etc...
Allow for cell merging
Allow for formatting (bolding in this case) of a portion of the text inside of a cell while leaving the rest of the text unchanged
Image insertion/repositioning inside a cell (not crucial)
Multiple Worksheets per Workbook

These are all the features I can think of off hand, any help or suggestiong at alternative libraries to look at would be appreciated. We are running Excel 2007 on the server but we are rolling out Office 2010 to clients so I think that might open the doors for some more supported file formats, if that helps.

Solution

After looking through the various options and performing more independent research I ended up using EPPlus, which you can get @ http://epplus.codeplex.com.

Thanks for all the suggestions.