You need to cast sender as a UIButton:
-(IBAction)buttonPressed:(id)sender{
UIButton *button = (UIButton *)sender;
NSLog(@"%d", [button tag]);
}
Edit: Regarding the message "unrecognized selector"...
Based on your error message, it's not able to call the buttonPressed method in the first place. Notice in the error message it is looking for "buttonPressed" (no colon at end) but the method is named "buttonPressed:". If you are setting the button target in code, make sure the selector is set to buttonPressed: instead of just buttonPressed. If you are setting the target in IB, the xib may be out of sync with the code.
Also, your original code "[sender tag]" should also work but to access button-specific properties, you'll still need to cast it to UIButton.