Tiff - a visual typeface diff tool.
A type diff tool that visually contrasts the differences between two fonts.
Type Scale - A Visual Calculator
The Grid System
The grid system is an aid, not a guarantee. It permits a number of possible uses and each designer can look for a solution appropriate to his personal style. But one must learn how to use the grid; it is an art that requires practice.
Gridulator: Make pixel grids, lickety-split
Tell Gridulator your layout width and the number of columns you want, and it’ll spit back all the possible grids that have nice, round integers
Web Font Specimen
See how type looks on the web