If you create a link list (default lists type: 103), the way to add a new SPListItem by code is quite tricky.
If you want to add an new url to this links list with these meta data:
Description: tom's blog
you'll notice that there is no description property.
the example below shows you how to add a new item:
SPList linkslist = web["links"];
SPListitem newlink = linkslist.Add();
newlink["URL"] = "http://tom.vangaever.be/blog, tom's blog";
NOTE: there must be a space after the comma, otherwise it won't work.
when you open the links list, you'll notice that the URL displayed is “tom's blog” and when you click on it… http://tom.vangaever.be/blog opens.