Jon as you've mentioned NGC 6210 , I would like to suggest you 3 more small bright planetary nebulae in the upcoming summer skies - NGC 6572 in Ophiuchus , NGC 6818 in Sagittarius and NGC 7009 in Aquarius . You may have observed all of them but still .
Actually they 4 are in my SkySafari observing list , but the weather here is exactly opposite to what someone would like ... I forgot what criteria I've filtered them . But I'm pretty they all have very high surface brightness , especially NGC 6572 . SkySafari says it has 100 times the surface brightness of M57 ! If someone can find them and give a report I will be very much pleased !