Solid State Drives
Assuming you are using a 64-bit OS with a 64-bit version of ADS, there should be not a practical limit to the amount of memory ADS will use., but adding more memory probably is not going to help, because it almost certainly depends on your overall database size.
An SSD could also provide a pretty decent performance improvement. One of the big performance improvements you get from an SSD is the elimination of latency (disk seeks and head movement). If you scan through a table in natural record order, there will probably be little difference in performance between an SSD and a traditional mechanical disk assuming they have equivalent bus speeds. But if you skip through a table in index order, then there can be a lot of disk seeks if the data is not already cached. An SSD can really speed that up.