The workflow I've settled on:

1. Start with any grayscale height texture (bricks, ripples, weave, etc.).
2. Convert it to a tangent-space normal map. Lately I use a small browser-based tool for this, normalmapbench.com, because it runs entirely locally (the texture never leaves the machine, which is handy for client work) and it previews the result under a movable light before you export a PNG. It also gives both OpenGL and DirectX variants.
3. In your renderer's material editor, load the normal map into the bump/normal slot, and keep the height map for displacement if the engine supports it.

Two things that tripped me up:

• Green channel direction matters. If the surface detail looks inverted, switch the Y convention (OpenGL vs DirectX) instead of fighting the intensity slider.
• Soften the source height map a little before converting. Noisy height data turns into sparkly, glittery normals under sharp sunlight.

Full disclosure: I built normalmapbench, so take the recommendation with a grain of salt — but the local-preview workflow is what I actually use on client models. How do others here generate normal maps for rendering work?