Grouping Nodes by first letter of field
Add the field a second time so it appears twice in Fields, check exclude from display and uncheck link this field to the original piece of content. Under rewrite results check trim this field to a maximum length, and enter 1 in the textfield.

Under format click settings next to unformatted list, etc. and select the right field in the grouping options.

You'll probably need to adjust the sort criteria too