One bag I travel with is the I travel with the Tumi Bridge 24 with the folowing dimensions: 17" x 24" x 12". Admitedly, it is larger than the offically allowable size, but it fits sideways in every overhaed I have attempted, although I am not sure I have been with it on the MD-80. It certainly fits on the 757s. This is a soft-sided (frameless) bag which is very versatile. I have never not got this on, although twice I have been given a hard time: once bya BA FA intra-Europe in CE, and once by an AA gate agent, who at first wouldn't allow it, and then after everyone had boarded and there was still room in the F overhead bins, it was allowed. I mostly use this for international flights when carrying it on in premium class in never an issue.

Otherwise, I travel with a conventional 21' wheeled bag, and that always fits. I think the bag I use is Studio, which I think was a Hartman sub-line bag, and it always fits.