This spider is a cobweb/comb-footed spider (family Theridiidae) in the genus Steatoda; likely Steatoda grossa. Often called the false widow spider, it is capable of inflicting a painful if mishandled - see http://tinyurl.com/23ladu6 for images and more detailed information. Just for the record, with the exception of one small family (Uloboridae), all spiders have venom glands and therefore technically are venomous. However, only a very few species have both potent enough venom and large enough fangs to pose any threat to human health.
I agree with suunto, in my opinion this is a false widow. Just to make a "plus" to his wonderful explanation: However a very few species have the "abiltiy" to life threat humans with their poison, is good to remeber that some people are allergic to bug bites and, although spiders are not tecnically "bugs", their bite can do iniciate a allergic process. So, be careful.