A back-pack type of carrier. We have one with a metal frame that I love. The strap type ones often have too many straps and are a pain to use (in my experience). I put my five month old in mine the other day and did the lawn and various other yard duties while he fell asleep on my back.

I used it all the time with our first son as well. He was geocaching with me at a very young age in that. I also took the two of them for a short, slow ride around the yard on my motorcycle the other day. The five month old on my back and the three year old on the back seat holding onto the frame of the rack.

A Bumbo.
Vibrating Bouncy Chair.
Video Monitor (ours was bought a geeks.com three and a half years ago)
A dehumidifier makes for a great white noise generator.
A play mat with stuff overhead to play with (sort of like a dome tent without the roof).
If you can find a place to buy patience... buy some!

Another bit of advice is to put the child in their own room early in the game. Our first was 5 weeks old and in his own room and our second was 4 weeks old. The first started sleeping through the night at 3 months and the second at 2 months and a bit. That also means you may sleep through the night and that can help a lot with patience for the rough days that the wee ones will have.

The last bit of advice is to enjoy it all! It goes so fast. Our three year old was a baby to us... and then the new little guy came along and we realized just how grown up our three year old was. Wow! Times files!!!