Google algorithm updates don’t seem to be anyone’s best friend except of course Google themselves! Almost every website in the world has been bitch slapped by a Google update at some point or another. With enough resources, time and contacts in the SEO industry, some sites are able to recover from a Google penalty and go on to thrive.
Others never know what hit them, don’t know what to do and give up in disgust. This need not happen to you. There are plenty of free resources like this site for instance, available on the Internet that will give you a good start. However, the more severe the penalty the more resources you might have to employ to get your site ranking and getting traffic again.
If you have a real desire to recover from a penalty these guys might be able to help.
Here’s another resource that has lots of information about recovering from Google updates.