Asking for a better cash price is a good basic negotiating tactic, but you can also score a bargain by asking for extra freebies when you're making a high value-purchase.
Matthew JC Powell, Mac guru extraordinaire and presenter of MacThePodcast, offers the following "JB Hi Fi haggling trick":
Before you head to the hardware dept, grab a couple of DVDs/BDs/other and just casually hang on to them while talking to sales dude about the hardware you want to buy. Ninety percent chance when you go to the register those discs will be thrown in for free without your even asking.
I haven't tried this one myself, but it sounds promising. If you've successfully deployed this or a similar negotiating tactic, share your victory in the comments. Thanks Matthew!