Topeak QR EX. It works fine but without the side adapters for panniers the capacity is a bit limited for me. I originally bought it during my early days of commuting because the old steel mountain bike I revived didn't have any braze-ons either and I eventually outgrew it for a "normal" day's commute. Some people have issues with those swaying but once attached mine stays put - I just tape the spacers on real tight and clamp it down.

I will say - and this is completely in vain - I prefer a more traditional look to my commuters and the beam rack tends to be a bit too "modern" of a look to me. It is functional, though.