Do not use SPList.Items.Add as this will get all items in the list before adding a new SPListItem.
Source: Aidan Garnish
NOTE: requires .NET 3.5 for System.Linq FirstOrDefault method, can be switched for a loop.
Source: Nick Grattan's SharePoint BlogThis code:
1. Gets a SPSite for the current site collection, and opens an SPWeb for the site.
2. Gets a SPList for the given list, and then an SPFolder for the root folder in this list. This code always creates the document in the root folder, but the code can easily be changed to place the document in any folder in the document library.
3. Gets a SPFileCollection for the documents in the folder.
4. "DocumentTemplateUrl" is used to return the Url of document template associated with the given content type.
5. Get an SPFile for the document template in spf and open it for binary access using OpenBinary
6. Add a new document to the folder through the SPFileCollection referenced by fcol.
7. Get an SPItem for the new document and set the "ContentType" column to ensure it uses the correct content type (it will default to the first content type in the document library).
8. Update the item and the added file.
9. The catch section checks for an -2130575257 error, which indicates the file already exists.
Source: Andy - novolocus.com
Note that the CAML to create the recurrence can be complicated so please take a look at the MSDN article.