I'll second this sentiment. Gmail catches an obscene amount of spam sent to my account accurately and with so few false positives it blows my mind. I've dealt with lots of anti-spam software and some hardware and Google does a fantastic job.
Pro tip: you have to just start flagging things with the convenient "this is spam" button and in a short time their filters figure it out.
OP might just be getting a lot of legitimate list traffic that they signed up for. That isn't spam, you asked for that and need to hit 'unsubscribe'.