My son was close to 4 when we had our second, but I did a few things that really seemed to work to keep the almost 4 year old happy.
First, my son and I went shopping and picked out a special outfit for the baby. This was HIS gift to the baby and he got to give it to the baby when they met for the first time.
Second, son and I made plans regarding what he could do to help out his busy Mom. I cleared out a low drawer in the kitchen (close to where I would nurse in the daytime) and filled it with burp rags and bibs. His "job" was to get me a bib or burp rag whenever I needed one. Granted, he often took a long time (I kept a similar stack right next to my seat) and I would no longer need what I had sent him to get, but it made him feel important and involved in the excitement of having a new member of the family. I also always made sure to thank him for helping. Nothing seems to work better with my boys than just acknowledging the good things they do, no matter how small!
I also put together a collection of really small gifts (mostly match box cars, since that was what interested him the most). If someone came over with a gift for the baby (and none for the older), he'd get to choose one of the wrapped small presents from the basket. He didn't care that it was something small (or cheap). He was just excited because he got a present, just like the baby.
I think just to being aware of what's going on with the older and keep communicating will keep most jealousy at bay. My son was pretty happy to go off and play on his own a lot of the time (after all, babies are pretty boring to them!), especially if when he did look for my attention, he got it or was promised a time soon when he could have my attention. Often just explaining why I couldn't play at the moment and promising to play once done with "X" was enough to make him happy.
I love the idea of the camera too. It could be a great thing for you to look at together when you're in between busy moments with the baby. If you go with the camera, you may want to consider having some photo scavenger hunt ideas at the ready. (I've done this with both my kids with great results.) Since he's probably not reading yet, put together some pages with some images of things he can find around the house. Make a game of him taking pictures of those same types of things around your house. It'll keep him busy and he'll love showing you the results when he's done!
Best of luck with your new addition!