IDCard is a simple addon to show item, spell and achievement icons next to the tooltip.
You can left-click and drag the icon to move the entire tooltip. Also, you can shift-click the icon to link the item in Chat, or control-click the icon to try on that item. With an achievement icon, control-clicking opens the achievement frame to that achievement.
Note to addon authors:
IDCard has the ability to support an arbitrary number of tooltips. To add auto-support to your addon's tooltip, just call IDCard:RegisterTooltip(tooltip) passing it your tooltip object.