Before deciding to buy, check the product cycle on the MacRumors Buyer's Guide. There might be an update about to launch (happens once or twice each year).
If you're self-employed or if you’ll use your iMac for business, ask to meet with someone from Apple’s business team (there’s a team in every store). Business purchases get a 5% discount, which can easily save you £100. The only requirement for the discount is that it’s your second business purchase from the store, so if you’ve bought something there in the past, search for your email receipt (or ask the store for help). Even if it’s your first Apple purchase, it’s worth opening a free business account for savings on anything you buy in future.
Don’t buy extra RAM from Apple. It’s extortionate. I got my machine with the minimum of 4GB RAM, then bought another 8GB through Crucial (arrived next day). Installation is simple, takes ten minutes, and doesn’t affect the validity of AppleCare. Crucial charged me £80 for 8GB. That would’ve been in the region of £500 from Apple.
I thought of adding a 256GB solid state drive to the 1TB hard drive to improve start-up times. But at £600 extra I gave it a miss. The i7 is already a powerful machine. More than enough for me.
Do you have any buying tips to share?