About the easiest to find and desirable to use 30 pin SIMMs are the 4MB size, 8 of which will get you 32MB of RAM in an SE/30 (which both of mine have). I could stuff more into them but don't see the need for it. If you run OS 6 on an SE/30 then 8 x 1MB would be perfect.

I would save the 8MB 30 pin SIMMs for machines with only 4 SIMM slots (as mentioned the IIsi).