Most polls are BS. If you want a polling service that has a history of being accurate, check these guys out:
Rasmussen Reports
Here is a
comparison of the polling results versus the actual results for the 2006 Senate races.
They also accurately predicted, within one percent point, the last two general election results. I don't think you'll find a better polling group than this.
With that said, no polling group (because of small sample size) will have impressive accuracy all the time. But Rasmussen Reports has the best record historically.