Visual studio of course… en..

You need to install Visual Studio Extensions for SharePoint, inorder to have a SharePoint Webpart ‘V S Template’. You can find the latest version @
http://www.microsoft.com/downloads/details.aspx?familyid=3E1DCCCD-1CCA-433A-BB4D-97B96BF7AB63&displaylang=en

Also, check out WSP Builder, it is of gr8 help to packaging your custom webparts, events etc.
http://www.codeplex.com/wspbuilder/Release/ProjectReleases.aspx?ReleaseId=11603

If you are a newbie and want to develop a web part quickly follow this post
http://www.u2u.info/Blogs/Patrick/Lists/Posts/Post.aspx?ID=1650