I've been very satisfied with the Sierra Designs Tengu 2 tent. I got an 07 model for about $160. It has an attached rain shell that can be raised for those too warm nights. The bottom tub is sealed and I've yet to get wet. It uses 2 poles for an external frame and I'd recommend getting either a footprint or make one as this will protect the bottom of the tent [better to trash a $10-25 footprint than a $160 tent].
Not all tents are true 2-man ones. The Tengu could be best described as a 1.5. Two in the tent would be very tight so I'd suggest a 3-man for 2 folks. By the time you put a pad/air mattress, bag, some personal items, and some goodies, the tent is quite full. Some folks go for the 4-man after deciding that the difference in pack size isn't that much.
The Tengu is 7"x21" and while too big for the panners is light enough for the top box rack. I found that I'd rather use the panners for carrying things that I don't want to get wet [sleeping bag, clothing, computer...]. I didn't care if the tent got wet as I knew that the inside would be dry and the tent would eventually dry out.
I'd look at how the tent is supported, how easy it is to raise, if it comes with tent pegs, if you can sit up in it [great for reading at night while in the sleeping bag], inner dimensions [make sure that there is enough length so you can stretch out without your head or feet hitting the sides of the tent], and if it suits your needs. I'd also recommend a mallet or hatchet to pound the tent pegs into the near-concrete dense ground.