Tachyons X-ray — debug & align objects to an 8 or 16px grid
Type Sample — identify and sample webfonts — 3 samples for free, or unlimited samples for $5/year subscription. available as a bookmarklet or Chrome extension
WhatFont? — inspect a webfont’s name, family, weight, size, style, color, line height, and source (if hosted via Google Fonts or Typekit)