Another battle between the Russians and Germans that seems similar is Battle of Tannenberg during WWI. Out of 206,000 men of the trapped Russian Second Army 78,000 were killed or wounded and 92,000 taken prisoner . However it seems Stalingrad still has the edge on this because both sides had their backs against the wall in 1942, whereas Tannenberg was a bit more one-sided.
The Battle of Seden destroyed an entire french army (mostly captured, not dead) and lost the Franco Prussian war for them but like Tannenberg was one sided and over quickly. An eastern example of a high casualty battles which outcome decided a large war is the Battle of Fei River (700,000 out of 870,000 deaths on the losing side according to the Book of Jin). But again this was fairly one sided.
So maybe encirclement isn't the important thing and it's about countries stubbornly pouring manpower into the meat-grinder of an "un-loseable" war of attrition. The Western Front of WWI is a great example (lots of decimated units here). Verdun being a particularly horrific fight over some hilly ground near Verdun-sur-Meuse. Loss at Verdun might have might have lost the war for the Allies, but didn't losw it (not immediately anyway) for Germany. Perhaps Stalingrad was more decisive than Verdun in particular, but if you compare it to the western front in general there are a lot of similarities.
As far as other important battles with horrible casualty rates go the Battle of Antietam and percentagewise more lethal Battle of Stones River are good American examples. Leipzig is a good example before industrialised warfare.
So while there are lots of examples of desperate fighting, encirclement and awful causalities. I would agree that given the intense struggle on both sides and it's decisive role in the Great Patriotic War (that's WW2) Stalingrad was fairly unique, with the western front in WW1 being the strongest contender in my mind.
 Source: Sweetman, John (2004), Tannenberg 1914 (1st ed.), London: Cassell, ISBN 978-0-304-35635-5 p158
 Somme example: the 1st Newfoundland Regiment suffered 91% casualties in the Somme, 801 men, 500 dead, 233 wounded, which puts it in second place to the 10th Battalion West Yorkshire on the same day but I can't find those numbers
[PS] Thought I would mention ambushes like the The Battle of Salsu (302,300 out of 305,000) or 'Quintilius Varus, give me back my legions!, but I don't think they can be compared to Stalingrad.