The latest development version of SDL is available via CVS:

cvs -d :pserver:guest@libsdl.org:/home/slouken/libsdl.org/cvs login
# No password, so just hit enter when prompted for a password
cvs -d :pserver:guest@libsdl.org:/home/slouken/libsdl.org/cvs checkout SDL

When you check a fresh copy of SDL out of CVS, you need to generate
the files used by make by running the "autogen.sh" script, which will
run aclocal, automake, autoconf and then run configure.

There is a web interface to cvs at http://www.libsdl.org/cgi/cvsweb.cgi