Standard 30-30 ammunition has a range of about 150 yards, after that it starts dropping pretty quick. From what I have seen on 30-30 charts, after 150 yards the drop is about an inch very 10 yards (30 feet). So its unlikey that someone will be using a 30-30 for 300+ yard shots.
For ranges that the 30-30 will be used at, I like the Nikon Buckmaster series in 3-9X40. Some people do not like Simmons scopes - but my son has a simmons on his 30-30 and it does just fine.
Some of the spots my kids and I hunt at, we can not see further then 50 feet. Trying to use a high powered scope would be self defeating.
For close range, you need open sights, or a 2 - 3X as the base power. For 100 yards a 6 - 9X would do just fine. So say a 2-6X40 or a 3-9X40 scope for a 30-30 for ranges less then 150 yards.
I have to agree with Screaming Eagle - for less then 100 yards, open sights should be considered. But having a scope does allow you to see if the deer is a butt buck, spike or a doe. Sometimes those short horns can be hard to see.