The most common ways for people to subscribe to a blog and its content are through RSS, Email and Twitter. Facebook pages are increasing in usage too.
This plugin places the above icons in a widget area and lets users enter their own feed or page URLs. It’s really simple but there’s lots of power under the hood.

You can get

Key Features:

1. Offers an attractive range of subscription options for your readers using familiar-looking icons.
2. Intuitive interface for editing options, including your feed/page URLs, widget title and icon sizes.
3. Independent handling across multiple widget instances, using WordPress 2.8’s new widget_class coolness.

You can get Subscription Options Plugin form here