The only data we have on the subject seems to be be dlanod's quote about disppearences every week (for ~500 weeks) and a quote form the books:
Pettigrew screamed that Sirius had betrayed the Potters for everyone to hear, and then killed twelve Muggles by blowing up the street with a Blasting Curse, which created a crater large enough that the sewer pipes were showing.
so if we say in a 1 on 1 duel there's the possibility for one death of a wizard and ~10 muggles. As well as this if groups fight as in the the Battle of the Department of Mysteries, then we have this source
Once there, the six D.A. members were cornered by a dozen Death Eaters, whom they managed to fend off until the Order of the Phoenix came to their rescue. In the skirmish, the prophecy was destroyed, Voldemort was seen by the Minister for Magic himself, eleven of the Death Eaters were captured, and Sirius Black was killed by his cousin.
Only one death again! Wizards can hold their own it seems. I'm inclined to say if Voldemort has his wits about him he'd go for pin-point strikes on wizarding families (less well defended than DA and Phoenix members) as well as more defended targets, whether on purpose or by happenstance.
I'd average it out to 5 wizards and 10 muggles a week, on average, as a maximum bound, any more is unsustainable. And 1:5 as a lower bound; Volde' doesn't like to shed wizarding blood if he can.
That then equates to 500 - 2,500 wizards, and 1,000-5,000 muggles. In total this is about 1.5K-7.5K, well within the standard deviation of the deaths per year in the UK, 1970-1981 so should have gone undetected statistically.
I'd guestimate we have significantly fewer for the second war, only a handful (maximum ~50?) though I'm shakey on the specifics. Most of these I think would be form the Battle of Hogwarts.
So I'd say ~1.6K-7.6K humans died during the two wizarding wars, most of the giants, and very few other magical beings to my knowledge.