I'll let someone else comment on the historical examples, but leeching is still in use as a modern medical treatment and is often more effective than its modern medical equivalents. In injuries where there's an excess of blood, and blood flow is congested, leeches are used to help draw it away (microsurgery, repairing amputations, etc.). Leech saliva has an anticoagulant property that prevents blood from clotting, which can also help prevent tissue necrosis, and help improve circulation for people with diabetes, and blood thinners exist that are made from synthetic leech saliva. There are a ton of applications for their use in modern times, as it still remains one of the least invasive ways to get blood out. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3757849/

There's also a rare medical condition called Polycythemia, which causes an excessive production of red blood cells, for which the treatment is often phelobotomy, or "bloodletting", so that too exists in modern medicine: http://emedicine.medscape.com/article/205039-treatment