What do people think of the designs? My favorites are the SI-as-galaxy icons by Marah (especially #125) and the gravitational-singularity-as-wings ones by strelac (especially #124) --and my lettering and SI-sigil, of course. I'm not sure the semiotics of using a gravitational singularity in the logo are entirely advisable, though. I also like #109, but only because it's kind of pretty.
the gravitational-singularity-as-wings ones by strelac
Those are my favorites.
If you have graphic design experience, check out the on-going logo design competition at 99designs for the Singularity Institute. There are still 6 days left to enter and be eligible to win the $295 prize if your design is selected. Tell your friends with graphic design experience too. There are very few submissions currently.
Note: This is a blind contest. Designers can only see their own entries. All designs will be revealed when the contest ends.
If you're interested at getting a peek at the designs, they will be online after the competition is over. This is standard practice in 99designs contests to prevent designers from contaminating each other and having all the designs drift in a certain direction.