We have been using the ER clone 6F11 (Novocastra/Vector) for a few years now and really like it.  Following HIER in a 98 degree waterbath for 40 minutes, we use the antibody at a dilution of 1:200 overnight with EnVision+ detection (DAKO) and DAB+ chromogen (DAKO).  I have never observed any non-specific staining with this antibody.  Please note that epithelial and mesenchymal cells in tissues other than breast can show ER staining.  Examples include endometrial glands, endometrial stromal cells, smooth muscle cells in myometrium, hepatocytes, and others.

R. Cartun