A very interesting blog entry, Alphabetical Paging on a SharePoint List View,
by Tom Clarkson, talks about grouping/paging items in a SharePoint list based on their first letter.
If you are just looking for the formula needed to create a calculated column that contains the first letter of the item’s Title, here it is:
=IF(ISNUMBER(VALUE(LEFT(Title,1))), 0, LEFT(Title,1))