Well, I'm going to disagree with most of the posters in this thread. I would not recommend buying a kit. Most are either missing something you need, or have stuff you don't need.
So, here are my thoughts:
1. The most expensive item you'll need, which doesn't come in the kits is a brewpot. If you already have one skip to #2. If not, there are lots of options available depending on your wallet. But, IMHO, you should buy at least an 8 gallon pot, for the incremental difference of the larger pot, it will be much more versatile. If you have the ability to buy and convert a keggle, that's my favorite. I also think a spout on your pot is invaluable. Many people have used the aluminum turkey fryer setup from home depot with great success.
2. Instant read thermometer - you may already have one in your kitchen, but no real need to buy anything special at this point.
3. Hydrometer and test jar (I prefer a wine thief to the test jar because it will allow you to pull your sample and test in the same vessel and then release the wort back where it came from or into a glass to drink. The kits only come with a jar if at all)
4. You'll need 2 buckets, a 6 gallon fermentor bucket and a five gallon bucket for bottling. For the bottling bucket, I'd use a HD homer bucket and add a spigot to it. Buy the spigots at the LHBS and drill the holes yourself. The fermentor bucket just needs to be a larger bucket to allow for fermentation. Any 6 gallon plastic bucket with a lid will do. It doesn't need a spigot (although I still like one) but will need a hole in the lid for your airlock or blow-off tube. You don't need a secondary fermentor at this point.
5. Airlock or blow-off tube. On some really active ferments an airlock can get blown out, so I like the blow-off tubes better. A Blow off tube is simply a piece of tubing attached where the airlock would go with the other end in a bucket of water or sanitizer.
6. About 6' of vinyl tubing
7. A bottle filler wand. (the spring loaded type)
8. A Bottle capper - whichever type floats your boat, they both work.
9. Bottles and caps - ask friends, family, and local bars for the bottles. Don't buy them. I usually buy the cheap misprint caps.
10. Starsan or Iodophor Sanitizer (I prefer Starsan)
11. I make my own PBW cleaner by mixing 60% Sun Oxy Cleaner and 40% TSP 90. This will soak labels and any other gunk off nicely.
12. Immersion or other chiller, not absolutely necessary, but it speeds up the brewing day and will help you make better beer. Immersion chillers are pretty easy and cheaper to make yourself.
13. Another "nice-to-have" is a bottling sanitizer injector. It really makes bottling more enjoyable.
14. Read either Palmer or Papazian's book or both. Palmer's book can also be found online, but I understand it is not as up-to-date.
I think if you price these items separately, (especially if you buy the buckets and tubing at Home Depot or elsewhere cheap) you'll come out cheaper and better than buying a kit.