Working with List Item Attachment

Here is some links about how to attach file for list item programmatically.

Uploading file(1) Creating a List Item instance programmatically using the object model

(2) Programatically upload a document in SharePoint 2010 document library

(3) Programmatically(C#) Adding, Deleting, Copying and Downloading Attachments in SPList

(4) SharePoint Gypsy: Develop a SharePoint 2007 Event Handler (Part 3)

(5) programmatically update a file in document library

(6) List Item Attachments – Handling the uploads manually.

Working with SPAttachmentCollection
(1) SPAttachmentCollection Class (Microsoft.SharePoint)

(2) SPAttachmentCollection.Add Method (Microsoft.SharePoint)

(3) SPAttachmentCollection.Item Property (Microsoft.SharePoint)

(4) Retrieving Attachments from SharePoint List Items

(5) c#: SPAttachmentCollection a collection of what exactly? - Stack Overflow

(6) How To Change The maximum file size Upload in SharePoint 2010

(7) SharePoint List Attachment Technical Brief

(8) Upload a File to a SharePoint Document Library - Part I