Hi,
If you could afford official course-ware, that would suffice in a testing perspective. As stated above, in addition you might want to refer to Junos-security, but the problem with junos security is it also covers topics which are above your JNCIS level so it prepares you for a jncip in a way. if you goal is to learn JNCIS then probably i would suggest weigh your options.
I have given exam a two days back and i have passed it on my second attempt, so make sure you got your nat, utm and policies are properly learnt.
Regards
Rakesh
https://r2079.wordpress.com