Ok, I misunderstood your requirement. In a transaction such as FB03, choosing the List... Export... Spreadsheet option will generally default to Excel (in MHTML Format). You can alternatively choose Select from All Available Formats and then in the drop-down choose one of the other Excel options (Office 2003 XML Format, Existing XXL Format, etc). If you like one of those, you will see the checkbox for Always Use Selected Format.
Alternatively, you can use Export... Local File instead, and then choose Spreadsheet as the format. Whereas the previous option would open the file immediately, this option will want to save it first, but you can choose the XLS format directly. It may or may not format as neatly as you like; the formatting is a bit different.
