You can use this web part as a starting point for all of your custom web parts
Especially since WSS 3.0 has been introduced, home-grown web parts have been more and more attractive to make. The hardest part is figuring out how to start them.
One option is to use a new class that simply inherits WebPart, that way everything is taken care of for you on the structure side. That is great, but then the actual building of the insides of the web part become much more convoluted; such as using a writer to output all sorts of strange .net html elements and implementing everything programatically outside the designer.
A much more intuitive way is to use an ascx (web user control) and design it just like a webpage. But the problem with that is the fact that it is a bit more complicated than that. Simply inheriting WebPart does not really do you any good, it will work, but you can't change and WebPart attribute such as TitleUrl, Description, TitleIconImageUrl, etc. The base Web Part properties.
The zip available below is a simple blank web part with inheritance taken care of all ready, you just start putting together your webpart like any other user control. Then all you need is to register it in your page like any other control:
<%@ Register src="~/WebParts/blank.ascx" TagName="blank" TagPrefix="wp" %>
And implement like you would any webpart:
<wp:blank ID="wpBlank" runat="server" Title="Blank Web Part" TitleUrl="http://naspinski.net" TitleIconImageUrl="http://naspinski.net/pics/blogengine.ico" />