Diagonal Seam Tape from @cluckclucksew.  I've tried a variety of tools to get accurate 1/4" seams and this has been the most effective for me.  This tape is intended for diagonal seams such as for Half Square Triangles (HSTs) or Flying Geese but I use it for plain straight seams for very accurate results.

Stripology XL Ruler from Creative Grids.  Total game changer.  Cut strips and pieces in a fraction of the time.

Flying Geese Square Up Rulers