Letter drills are easy for the goalie to remember and can keep the goalie busy while the coach's attention is elsewhere.  The goalie only has to remember U-V-W-X-Y.

All letter drills should be performed for about 30 seconds at a time and as fast as is possible while maintaining proper technique.

Goalie starts on the post.
Goalie then moves out to the top of the crease and out beyond the top of the crease.
Goalie backs up to the top of the crease then pivots to the other post.
Then repeats on the other post.
All pivots can be shuffle, t-glide, butterfly or stacked pads.