The max discount is $97. Any features like IPs, domains, etc... come out of that $97. So the more features you want, the lower the cash discount will be.
Promo codes are created by the users, so we can all make them. So the person whose code you use will get the credit for your sign-up.
It breaks down like this:
Each IP subtracts $30, each domain reg subtracts $15 and each 10% of disk space or bandwidth knocks of $9.
In the long term, if you have a use for them, the domain names & IPs are good deals.
So, you could do a code for 3 IPs ($90) and $7 off, which adds up to $97. Or any combo of the above.
If you want something specific, I (or anyone) can make a code.
Save up to $96 at Dreamhost with ALMOST97 promo code (I get $1).
Or save $97 with THEFULL97.