Squadron Seam Scraper - great tool for removing mould lines
Squadron Putty Applicator - simple sculpting tool for green stuff
Xuron 2175ET Sprue Cutter - thin flat sheer cutter, great for cutting models out of spures
You need good brushes. Not only do they impact the quality of your work, they also impact quality of your life.
For your regular work horse brushes I recommend the Winsor & Newton Series 7 Kolinsky Sable brushes:
You will need for basic painting and detail work #1, #0, #00 and #000. You may also want to pick oup some larger ones for base-coating and ink application.
Sometimes you may also want a trash set for experimenting with different paints, or doing rough work such as painting textured bases.
When you need to paint eyes on your models:
TAMIYA 87153 - a pointed ulta-fine brush for painting eyes and detail
The Army Painter Psycho - another super fine pointed detailer brush
You’ll also need some siff synthetic bristle brushes for drybrushing work:
The Army Painter BR7015 - a large flat brush
The Army Painter BR7010 - a large angled drybrush
The Army Painter BR700 - a small angled drybrush
Drybrushing absolutely wrecks sable brushes. Synthetic holds up longer.