~GE Silicone I~
That's what you want, it's the II that TAF CAF and Carl are talking about, it has anti mildew stuff in it and will leach out into the aquarium. It's about $4 for a 10oz tube vs 3oz tube from LFS for the same price or more.
Edit: I just wanted to add that Im speaking from tons of research and personal experience. I resealed my 55G using this and it holds great although Im not the best at laying a smooth bead. Also wanted to add that this stuff has about the highest adhesion properties to glass versus anything else. It took 1.5 tubes (15oz) of it to lay a nice thick bead all around my 55G.
Dunno if you have experience with resealing or not but, make sure there is no old silicone left although there will most likely be a few small areas with a thin film that just refuses to come up. Everyone reccomends using either acetone or alcohol to clean the glass before laying the silicone. I imagine paint thinner would work even better, it would also remove that little thin film of old silicone but, I doubt it's safe to use on the aquarium.
Goodluck, hope this helped.