I'm looking for a strong glue/epoxy that will hold to rubber, anyone have any ideas? Thanks a lot!

There are a number of adhesives that should work. It partly depends on what you're gluing rubber to. One possibility is Shoe Goo, another is marine epoxy.

In addition to the fine answer above, I would think that it would also depend on the type of rubber that you are trying to adhere to a surface as well as if there will be any tension created between the points of adhesion after the adhesion between the two surfaces has been accomplished.

My wife is trying to glue swarovski crystals to the rubber strap on flip-flops, she has tried a few different glues and to no avail. Any help is greatly appreciated, she is driving me crazy with this stuff.

Since flex is a factor, I suggest ShoeGoo. I glued rubber soles back to leather shoes with it and it lasted sev months until I needed new shoes for other reasons.

Does shoegoo dry clear?

As I remember, yes, it dries clear.

Great! She looked it up and I think she is going to order it tomorrow, seems to be what she is looking for. Thanks a lot!