I have a UITableView with 5 UITableViewCells. Each cell contains a UIButton which is set up as follows:
- (UITableView         
        I would use the tag property like you said, setting the tag like so:
[button setTag:indexPath.row];
then getting the tag inside of the buttonPressedAction like so:
((UIButton *)sender).tag
Or
UIButton *button = (UIButton *)sender; 
button.tag;
Chris Schwerdt's solution but then in Swift worked for me:
@IBAction func rateButtonTapped(sender: UIButton) {
    let buttonPosition : CGPoint = sender.convertPoint(CGPointZero, toView: self.ratingTableView)
    let indexPath : NSIndexPath = self.ratingTableView.indexPathForRowAtPoint(buttonPosition)!
    print(sender.tag)
    print(indexPath.row)
}
you can use the tag pattern:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
     NSString *identifier = @"identifier";
     UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:identifier];
     if (cell == nil) {
         cell = [[UITableView alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:identifier];
         [cell autorelelase];
         UIButton *button = [[UIButton alloc] initWithFrame:CGRectMake(10, 5, 40, 20)];
         [button addTarget:self action:@selector(buttonPressedAction:) forControlEvents:UIControlEventTouchUpInside];
         [button setTag:[indexPath row]]; //use the row as the current tag
         [cell.contentView addSubview:button];
         [button release];
     }
     UIButton *button = (UIButton *)[cell viewWithTag:[indexPath row]]; //use [indexPath row]
     [button setTitle:@"Edit" forState:UIControlStateNormal];
     return cell;
}
- (void)buttonPressedAction:(id)sender
{
    UIButton *button = (UIButton *)sender;
    //button.tag has the row number (you can convert it to indexPath)
}
A slight variation on Cocoanuts answer (that helped me solve this) when the button was in the footer of a table (which prevents you from finding the 'clicked cell':
-(IBAction) buttonAction:(id)sender;
{
    id parent1 = [sender superview];   // UiTableViewCellContentView
    id parent2 = [parent1 superview];  // custom cell containing the content view
    id parent3 = [parent2 superview];  // UITableView containing the cell
    id parent4 = [parent3 superview];  // UIView containing the table
    UIView *myContentView = (UIView *)parent1;
    UITableViewCell *myTableCell = (UITableViewCell *)parent2;
    UITableView *myTable = (UITableView *)parent3;
    UIView *mainView = (UIView *)parent4;
    CGRect footerViewRect = myTableCell.frame;
    CGRect rect3 = [myTable convertRect:footerViewRect toView:mainView];    
    [cc doSomethingOnScreenAtY:rect3.origin.y];
}
func buttonAction(sender:UIButton!)
    {
        var position: CGPoint = sender.convertPoint(CGPointZero, toView: self.tablevw)
        let indexPath = self.tablevw.indexPathForRowAtPoint(position)
        let cell: TableViewCell = tablevw.cellForRowAtIndexPath(indexPath!) as TableViewCell
        println(indexPath?.row)
        println("Button tapped")
    }
A better way would be to subclass your button and add a indexPath property to it.
//Implement a subclass for UIButton.
@interface NewButton:UIButton
@property(nonatomic, strong) NSIndexPath *indexPath;
Make your button of type NewButton in the XIB or in the code whereever you are initializing them.
Then in the cellForRowAtIndexPath put the following line of code.
button.indexPath = indexPath;
return cell; //As usual
Now in your IBAction
-(IBAction)buttonClicked:(id)sender{
   NewButton *button = (NewButton *)sender;
//Now access the indexPath by buttons property..
   NSIndexPath *indexPath = button.indexPath; //:)
}