.NET Resource Leak Gotchas

Question

There are several ways that developers can get caught out by unintentional resource leaks in .NET. I thought it would be useful to gather them in one place.

Please add yours with one answer per item, so the best get voted up :)

Answer 1

Easy memory leak: make a static field in a class of type List. Add items to List. They'll never get garbage collected, so unless you remember to manually remove your items when you're done with them, the memory is permenantly tied up.

Answer 2

P/Invoking to unmanaged code, and not cleaning them up, or not implementing IDisposable to get them cleaned up.