Visual Studio Extensions
If you want to write your own Webpart, you can start from scratch with a Class Library, or use the templates from http://www.microsoft.com/downloads/details.aspx?FamilyID=19f21e5e-b715-4f0c-b959-8c6dcbdc1057&DisplayLang=en
The downside of this VS templates is, that they can only be used on a computer, which has SharePoint installed, and you cannot open a project created with the VS templates with a VS on which the templates are not installed.
Server side controls
Ishai Sagi wrote a great article about Webpart development. His article is about server side controls and data binding in Webparts.
Here is the link to his great article: http://feeds.feedburner.com/~r/sharepointmvpblogs/~3/106217340/server-side-controls-and-data-binding.html
Mike Ammerlaan shows in his article how to integrate Ajax in SharePoint, and how to create a simple Ajax Webpart.
He also explains how to use UpdatePanels with Ajax, and how to disable the default SharePoint form action.
In this post I’m going to explain how to start using ajax in your web parts. The goal of this article is to reproduce functionality similar to the KPI and BDC web parts in MOSS 2007. If you don’t know what ajax is or the basics of how it works this article is probably not for you.