There are a lot of good posts here, and I agree with most. For me it boils down to five things you need to consider when putting together your wardrobe in a way that you don't end up wasting money on tons of different pieces and only wearing a few.
One - Layers, Layers, Layers!
You can always peel things off or add one on to adjust.
Two - Base Layer!
As already mentioned, never wear cotton, especially against your skin. There is something to be said about the higher end base layers like Under Armour, but as long as it is a synthetic that wicks, and is not to thick (again with the layers), you have the right foundation. If your base doesn't wick moisture, you can have the best rain suit in the world, and you will still end up cold and wet from sweat. I like long sleeve base layers for all seasons, as you can always roll sleeves up in the hot sun, or roll them down in the bitter cold winter mornings.
Three - Shell that is light, waterproof, and has pit zips.
This is wear you get what you pay for in extreme conditions. Not all waterproof jackets/pants are made the same. Most will keep you dry in a straight down rain, but when busting brush (wear water can be forced up in weird directions, and is allowed to pool) cheaper jackets will leak. I like to wear a light thin rain jacket (again layers), which allows me to put on and off pieces underneath. Also, never buy a jacket that doesn't have pit zips (the odd zippers under your arms). This allows you to vent yourself when walking or hiking, and dramatically reduces the amount your body sweats, so that when you get to where you are going to sit, you just close them down and you are not a sweaty mess, and the heat is now trapped in your jacket. I wish more pants had this feature (I think I have only seen it on some River West pants). I like the Cabelas MT050 for big game hunting in the cascades, best stuff I have ever seen used, but spendy.
Four - Boots
The number one thing that is always exposed to moisture and the cold no matter if it is raining/snowing. Invest in a decent pair of boots that get real good field tested reviews. Don't buy into the hype. Also, make sure they are light weight and easy to walk in.
Five - Pockets, Pockets, Pockets.
There are some really good rain jackets/pants out there that are affordable, but don't have enough pockets. Specifically the pants. If hunting pants don't have cargo pockets, don't buy them. Convienence is key here. If you can put it in a pocket, thats one less thing to put in your pack, or a way to not even carry a pack. Also, look for the leg zippers to aid in the layering process....easier on and off.
As for camo, this is all preference. As long as your outline is broke up your in business. Sit in or against a bush, and your done. The only time I think it really makes a difference is if your hunting in a snow covered field (you don't want to be that one dark spot sitting against a snow bank). I like the sheet idea one of the earlier posts came up with (again with the layers).
The above is how I try and buy hunting clothes, so that I can use them for all types of hunting and try and keep my costs down. With that said, I like buying anything camo, so I am not one to always follow my advise.
Hope this helps and pulls together allot of the earlier posts to the fundamentals and not the brands.