it depends how you want the army to play. if your just looking for effectiveness then i direct you to this analysis:
http://www.dakkadakka.com/wiki/en/Chaos+Space+Marines+Tactica
the summary is:
demon princes very very good
obliterators very very good
cult marines good
terminators, raptors and havocs ok
most other stuff bad
dreadnoughts very very bad
possessed very very bad
demons (as in generic, not the new codex) very very bad.
while i dont necessarily agree with everything its still worth reading.
in casual games that your not to bothered about winning or losing then you can make pretty much anything work.
ive seen lists that run 3 squads of terminators, 6 land raiders and some token squads of marines. they do fantastically against some armies but terribly against others. there are a few rules (i use the term 'rules' loosely as you will probably find at least a couple of dozen people that dissagree with me) you should be aware of when building chaos armies:
1) In almost all circumstances, cult marines (plague marines, noise marines, khorne berserkers and thousand sons) are superior to standard
CSM.
2) Squads given icons should be large so that the cost per model of the icon is reduced without the squad loosing effectiveness.
3) Demon princes are the best
HQ choice chaos has avaliable. The are a similar cost to other
HQs but far better.
4) Dont be afraid to build powerful lists. People call certain things cheese but you should ignore them. In a highly competitive gaming enviroment a powerful build will win you more games. (Be aware that if you use power builds too often in casual situation people will stop playing with you, but this depends on your attitude too)
5) Drednoughts and possessed are terrible. Even if you think they look good on paper, i can assure you that they arent. you can take other options for less points that perform more effectively. Dont take them.