There sure are. While the Big Bang theory is probably the most widely known and accepted theory surrounding the origins of the current universe, there are still other theories being explored and proposed. Some of these are much more scientifically feasible than others; take a look around the Web and you can find lots of different ideas out there. One alternative that has received notable attention describes the universe as a continuous cycle of expansion and rebirth; the expansion period, similar to that described in the Big Bang, is followed by a period in which the universe once again becomes a dense mass of condensed matter, and then the expansion begins again.
The Big Bang theory postulates that the universe began as a singularity about four billion years ago, expanding rapidly and eventually forming the stars, galaxies, planets and everything else we see.