Additional domains - 301 redirect or change DNS servers? (or something else?)

If I own a site and have registered additional related domains which I would like to send users to my site, how it is best to set this up:

A) Change the DNS servers on the additional domains and have my hosting company
Example: OttawaMortgages.ca and CanadianPrivateMortgages.ca
(I'm guessing this is bad because it seems to be a duplicated site on a different domain... not only is duplicate content bad, but inbound link juice is being split between 2 sites instead of directed one powerful site - is my understanding of this correct?)

B) 301 Redirect the additional domains to the main site
Example: Gogle.com is 301 redirected to Google.com

C) 302 Redirect the additional domains to the main site
Example: Sales.ca is 302 redirected to BuySell.com
(Why would they use a 302 instead of a 301?? Source: http://www.seoconsultants.com/tools/headers.asp)

D) Like in the following example...
Example: ComputerSoftware.com somehow brings me to www.iris.co.uk, but according to the seoconsultants link above, it is neither a 301 or 302 redirect... ComputerSoftware.com returns a header status code of "200 OK"
(How does that work?)

E) Some other method???

Thanks in advance for answers...

A: Bad - as you say you risk dup' content penalties.
B: OK But - what's the point of acquiring additional domain names simply to redirect them? Unless you get backlinks to those domain names (unlikely since they will be redirecting) the only traffic you will gain is type-in (exceptions would be if the domains are pre-registered and have backlinks/ranks, then you would gain from the historical links so long as they remain in place).
C: Don't see much point in this - it's like a 301 but "temporary".
D: They (and you) could be using domain forwarding (if your registrar allows it). In practice it works somerthing like a 301 - DNS simply forwards to the target domain and the target domain is what will be shown in the browser address bar (so no risk of dup' content penalty).
E: Build another site and use as a doorway domain is about the only other option I can think of but I'm not a big fan... Unless you can afford to build hundreds and spread the hosting globally, you are just soaking up resources (time and effort) that could be spent building your main site bigger and better.

Honestly the best reasons I can think of to but additional domains (excluding pre-registered) are:
1. To prevent others from registering similar domain names (eg: buying all main .tld's or slight variations of your domain name).
2. To gain type-in traffic (but most decent type-in domains are gone nowadays)!