Following are the search technologies available for the SharePoint 2010

Microsoft SharePoint Foundation 2010 Search:

Microsoft SharePoint Foundation 2010 provides built-in-search for SharePoint site collection
SharePoint Foundation 2010 search should be considered if

• The organization doesn’t require enterprise wide search or searching external data sources

• You do not need a search to be scoped beyond the site collection level

• Your budget doesn’t allow you to purchase additional search capabilities
  

Microsoft Search Server Express:

Microsoft Search Server Express is a free downloadable product that provides search over enterprise content.

Consider Microsoft Search Server Express if you want an entry-level departmental solution where a single server meets your demand.

Microsoft Search Server 2010:

Microsoft Search Server 2010 is an enterprise wide product that can scale to multiple servers.

Consider Search Server 2010 if you need an enterprise-scale search solution that supports multiple crawls servers and query servers. Search Server is suitable for deployment in a large network.

Microsoft SharePoint Search Server 2010:

Microsoft SharePoint Search Server 2010 includes all the features available in Search Server 2010 and provides additional advantage of being tightly integrated with SharePoint Productivity tools such as social networking features and managed taxonomy

FAST Search Server 2010 for SharePoint

Microsoft FAST Search Server 2010 for SharePoint includes all the search features and integration capabilities of SharePoint Server 2010 and adds deep platform flexibility and scale and enhanced content processing capabilities.

Consider using FAST Search Server 2010 for SharePoint in your environment if you:
Require great scalability and performance

• Require an enriched enterprise search experience with the ability to customize and tune relevancy and navigation
• Have to crawl different types of internal and external content sources, including large-scale web content.
• Want to use sophisticated content processing such as property extraction

Also you can deploy FAST Search Server 2010 for SharePoint across multiple servers to meet demanding requirements for redundancy, performance, and capacity.

It can be scaled along the following axes:

• Document Volume
• Query Volume
• Processing Power of content, query and results

Cheers,

Kishore Kumar.N