What strategies and tools are useful for finding memory leaks in .NET?

I use Scitech's MemProfiler when I suspect a memory leak.

So far, I have found it to be very reliable and powerful. It has saved my bacon on at least one occasion.

The GC works very well in .NET IMO, but just like any other language or platform, if you write bad code, bad things happen.

Just for the forgetting-to-dispose problem, try the solution described in this blog post. Here's the essence:

    public void Dispose ()
    {
        // Dispose logic here ...

        // It's a bad error if someone forgets to call Dispose,
        // so in Debug builds, we put a finalizer in to detect
        // the error. If Dispose is called, we suppress the
        // finalizer.
#if DEBUG
        GC.SuppressFinalize(this);
#endif
    }

#if DEBUG
    ~TimedLock()
    {
        // If this finalizer runs, someone somewhere failed to
        // call Dispose, which means we've failed to leave
        // a monitor!
        System.Diagnostics.Debug.Fail("Undisposed lock");
    }
#endif