Glacial Augment and GA Hextech GLP Annie is so Good!
This combination is so good for Annie.
First off, Annie can rotate her stun and Glacial Augment's slow to forever keep enemies within her range to keep dealing damage and kill everyone. The true magic shines through once you complete your Hextech GLP with the super satisfying freeze rays, 65% slow goodness letting you get into range to stun them and kill them, you do not need Flash if you have some way to get into spell range, and the range of Hextech GLP and the slow does just that.
Technically you could just use Hextech GLP on it own, but then it is very lackluster without the freeze ray trails, which is why I think the active should just have the freeze rays implemented into it as the slow when the frost bolts hit an enemy champion since there is a massive difference in power between no GA keystone and with it.
On a personal preference, I want spell vamp, 45% cdr, magical boots, and biscuits for the extra mana pool for Annie and even 2.5% base spell vamp is enough sustain to help Annie through the laning phase, better once you start getting some kills or assists (spell vamp is very strong with Annie) so I am basically locked into Domination and Inspiration mastery pages for her. In general, Annie is locked to having Inspiration as one of her pages since if you do not go magical boots then you are taking hexflash instead.
Anyways, Hextech GLP and Glacial Augment is very strong for Annie and gives her tools to get into range to kill her foes, or force a Flash for landing the GLP frost bolts and saving your Flash to keep yourself alive.
P.S. Makes no sense to why Annie's attack speed is 0.579, should be 0.679, this only made sense back when Annie has 625 attack range, but Riot forgot to increase her attack speed when her attack range got nerfed.
P.P.S. Max E second, the damage reduction shield is significantly more important to have over 35 more damage on W plus you save on mana this way to charge your passive with.