iOS/Android: Instagram is releasing a major update today, allowing you to adjust how much of a filter you apply to a photo, along with other editing tools.
The filter slider is a very nice touch, letting you apply much more subtle filters. You can also adjust brightness, contrast, warmth, saturation, highlights, shadows, sharpen, and vignette (which darkens the corners of your photo). After you take a photo, just tap the wrench icon to bring up all your options.
The update should be available today for Android and iOS, although we aren't seeing it just yet.
Introducing New Creative Tools on Instagram [Instagram Blog]