A Scalability checklist?

Hi everyone, I'm researching on Scalability for a college paper, and found this site great, but it has too many tips, articles and the like, but I can't see a hierarchical organization of subjects, I would need something like a checklist of things or fields, or technologies to take into account when assesing scalability.

So far I've identified these:

- Hardware scalability:
- scale out
- scale up

- Cache
What types of cache are there? app-level, os-level, network-level, I/O-level?
- Load Balancing
- DB Clustering

Am I missing something important? (I'm sure I am)
I don't expect you to give a lecture here, but maybe point some things out, give me some useful links...