Hotkey: Ctrl+Shift+G
When you've got an invalid brush in your map, some compile tools will give you the id number of the brush that is bad. For example, Zoner's Half-Life compile tools will give you something like this error:
Entity 0, Brush 4, Side 8: has a coplanar plane at (304, -384, 0), texture GENERIC99
To find the invalid brush in your map, you'd just bring up the Go To Brush dialog (by pressing Ctrl+Shift+G) and enter 0 as the entity number and 4 as the brush number, then press OK. The invalid brush will become selected and centered in the 2D views.
Note: if you've compiled or exported your map with the "visible objects only" setting enabled, you should enable the "Search visible brushes only" setting here as well.