Twitter turned off their RSS support last month. This page gives several ways to create new RSS feeds for Twitter accounts.
Update (October 27, 2014): Here is a cost-free and ad-free Android app that is an RSS feed generator for Twitter.
Update (April 25, 2015): Here is a list of RSS feeds for each of my Twitter accounts, hosted by BazQux.
Here are links to RSS feeds for my daily tip accounts that were created using rss4twitter.
AlgebraFact (Algebra, number theory, miscellaneous)
Diff_eq (Differential equations)
TopologyFact (Topology and geometry)
AnalysisFact (Analysis: real, complex, functional, etc.)
CompSciFact (Computer science and programming)
UnixToolTip (Unix command line tools, Emacs, etc.)
SciPyTip (Scientific computing and Python)
RegexTip (Regular expressions)
TeXtip (TeX, LaTeX, and typography)