FASM
This is not an Tutorial but it is very helpful:
http://flatassembler.net/docs.php?article=manual
consider also to take a look at the examples that comes with the language.
There is also a forum with plenty of informations (about various Topics)
http://board.flatassembler.net/index.php
Here is a Beginner FAQ with all relavant informations for beginners:
http://board.flatassembler.net/topic.php?t=2530