To create a Custom Property for a Sandboxed Visual Web part, you can make use of the below code and link,
[WebBrowsable(true), Personalizable(true)]
public string ListName { get; set; }
Source
Using the above custom property value, find out the ListRssUrl and pass it to the below function to get the data from it.
Here is a small code snippet to parse sharepoint blog posts list’s Rss feed.
protected string GetRSS(string ListRssUrl)
{
string rss_text = “”;
string title = “”;
string link = “”;
string description = “”;
XPathDocument doc = new XPathDocument(ListRssUrl);
XPathNavigator nav = doc.CreateNavigator();
XPathNodeIterator items = nav.Select(“//item”);
while (items.MoveNext())
{
XPathNavigator navCurrent = items.Current;
title = navCurrent.SelectSingleNode(“title”).InnerXml;
link = navCurrent.SelectSingleNode(“link”).InnerXml;
description = navCurrent.SelectSingleNode(“description”).InnerXml;
}
}
Source
In your webpart, you can use a grid to display the title, link, description, etc.
Hope this helps you.