The most common recommendation I've heard is the 870 Police model with a Surefire tactical forend on the front. I would suggest you check out website such as
www.thehighroad.org and
www.thefiringline.com for more info.
I would suggest not buying anything until you've taken the proper safety and home defense courses. The NRA offers several of them that are extremely useful, and will put you in the proper mindset. You'll want to consider where you're located, what happens if a round goes through your wall, and other things.
Given what I've researched, I would personally go with a Remington 870 Police Model with the Surfire forend, and a 1911 loaded with MagSafe rounds by the bedstand. Both would be used extensively in practice so that I would be comfortable using them first.