How do you like this one: http://students.mimuw.edu.pl/~ksoltys/tcs.gif ?
When you draw this little line between sigma and the infinity symbol, you get a wind-up sigma ;) which I think is a nice symbol for TCS. I used this logo for TCS students' club in my department, but I think it wouldn't conflict. 

![alt text][1]


  [1]: https://i.sstatic.net/whNQ9.gif