Stuart Rothenberg, one of the two most famous American electoral handicappers (the other is Charlie Cook) is predicting a Republican wave in the upcoming Senate elections–sort of. Rothenberg makes clear that his numbers do not at this point show such a thing happening. But he also makes clear that he has been observing elections for a very long time, and that his instincts tell him this is going to happen. He also admits, however, that his instincts may revise themselves in light of further data. You can read what he has to say about it all here.
For the moment, the generic polls seem to lend support to his hunch. They are summarized here at Real Clear Politics. The generic poll has often understated Republican performance, so the fact that the GOP is actually ahead in so many of these polls is telling.
As usual, however, we have to remember that the only poll that really matters is the one taken on election day.