I agree that a synth bag is the right choice for a really challenging environment like the Arctic, or for environments where it's likely to rain a great deal without access to a dryer to dry a down bag out, or you're going canoeing or kayaking with the bag. Down is tough to get dry once it's wet.
For me, though, a down bag with a silk liner (mine is the 20 degree REI Sub Kilo model) is so much more convenient and long-lasting (down has better longevity than synth fills) that I take the risk of getting the bag wet. The small pack size is good as well, not to mention the lower weight. If you do get down, make sure it's at least 600 fill power.
As sleeping pads go, I'm hooked on Thermarests. They're air filled via a valve at one end, so bring a patch kit if you use one. You might consider a larger one than you'd take backpacking, since weight is less of an issue. Mine:
http://www.rei.com/product/734496
As for tents, I heartily agree that you're going to want a 2-person tent for yourself, and you will want something tall enough to sit up in. That rules out the "tunnel style" varieties, which tend to have two hooped poles, one near the feet and one near the shoulders. A little more weight and size is worth not waking up screaming claustrophobically in the middle of the night--ask me how I know! Also, you are going to want something that is freestanding--i.e. doesn't need stakes to pitch, but relies on its pole configuration to hold it up. When you're so exhausted that you end up pitching that tent in a dark parking lot in the middle of Wyoming, or are camping on slickrock in Utah, you'll appreciate this feature.
A full rain fly is necessary, of course, especially if it has a large vestibule--the space between the rain fly and the tent itself. This is often a good place to stow boots and gear.
A footprint that fits the tent (or one that you've cut from thin vinyl yardage or an old shower curtain) without sticking out past the sides is a very good idea for tent longevity and less dampness, too.
Aluminum poles are a must in a tent. Anything with fiberglass poles is crap; those poles will snap and splinter at the worst possible time.
Also, buy some seam sealer, set that tent up outside, and seal the seams (especially the ones between the floor and the sides). Helps it to not leak in the rain.
The REI Quarterdome is a solid choice; I like Sierra Designs tents, too. I've got an old 2-person Sierra Designs Night Watch tent that has been all over the US and Europe, has survived weeklong rainstorms with barely a leak, has been taken snow camping, survived horrible windstorms, sets up in 7 minutes, and is plenty roomy. Sierra Designs tents at REI:
http://www.rei.com/search?search=si...s+tent^cat,4500457:2-Person+Backpacking+Tents
I also have a Mountainsmith Boundary 2-person tent that is less well-built, but just fine for the job most of the time. Sometimes I even camp in it with my sweetie, but it's a tight fit for both of us! That one is no longer available, though.
Mountainsmith tent, bike and aforementioned sweetie:
The MSR Hubba Hubba tent has a good reputation as well, if you're looking for a tent with lots of ventilation--it's all mesh.
http://www.rei.com/product/781511