I went with boost and oil temp on a dual cloumn mount pod. If you already have boost, you could go oil temp and oil pressure. There are a lot of different opinions on weather or not its better to have oil temp or oil pressure. I went with temp because, for me, I would rather know when the car is warmed up to operating level so I dont drive hard when the engine is still cold. EGT is also very popular with stage 2, but I was too much of a wuss to drill and tap my exhaust manifold- I have heard they can crack because they are cast iron.
I think if people are going to do 2 pods the most popular is boost and EGT, and the triple pods are boost EGT and oil temp. Check out www.j-spectuning.com for dual gauge packages.