Database administrators are searching for that one tool that will make them productive and hands off of their day to day database management tasks. Oracle, SQL Server and other databases come with their own tool sets but the tools do not completely address the database monitoring software needs of today's dbas.
If you are searching for a basic monitoring script, you can find many combinations of scripts on the web. But if you are looking for a true database monitoring software, you have many free and expensive options for the oracle database including Oracle Enterprise Manager, Quest, BMC, HP, Manage Engine, zenoss, Hyperic and other related tools.
Selecting a database monitoring software can be a tedious and confusing task, focus on what you are trying to achieve from the tool and not on the bells and whistles. Oracle Enterprise Manager ( OEM ) is a great tool to get started with if your environment is primarily centered around oracle. Many tools offer integrated approaches to database monitoring so if your unix, windows and other teams are also acquiring their own tools, its best to combine your efforts and look at the new generation open source tools like zenoss etc.