My computer's in the shop and I'm in the midst of a terrible depressed episode, so my superpowers are confined to knitting and lying deathly still. I thought a little writing might do me some good, and since I'm putting my crazy new iPhone camera to work taking pictures of my knitting and describing what I'm doing, I thought I'd write on that subject.
As I've said before, I'm a "think globally, act locally" kind of girl. That said, I've only recently realized that I live in Texas. Last year's winter was so mild that my hot water never ran out while I showered, and I can do some marathon showering sessions. That isn't to say that we haven't had some nasty winters--we're mostly known for ice storms and not snowstorms--but Texas may not be the place for an inundation of wool hats. If you're in the same predicament I am, you may consider giving to this place in New York (they haven't updated their website in years, so I suggest contacting them beforehand) or this place in Minneapolis. My personal choice for the year was the realization that my hometown of Columbia, MO, gets considerably colder than Denton, TX, so to Columbia my knitting shall go this year.
You don't need a big, fancy organization that specializes in hat-knitting for your purposes. All you need is a local (or less-than-local) homeless shelter. I have in the past given my hats to the Salvation Army Shelter, which is the only homeless shelter in Denton County (!), and they have no official charity or "program" for such giving. Often shelters will have lists of the things they need, but that may be about as official as it gets. So don't be afraid to still create and donate in your area.
There's a hierarchy, I've learned, to what's needed: Anyone can knit a scarf. I'm not saying that scarves aren't needed, just not in the abundance at which they can be churned out. Heck, I'm knitting a scarf right now--it's a great way to use yarn ends. Hats are probably the most needed item--I mean, who leaves the house in winter without a trusty hat on? I'm aware that knitting hats is not the easiest thing in the world, but that's why Knifty Knitters exist. And boy howdy, using the basic stitch you can make a bazillion hats in no time flat! I knit exclusively on knitting looms (can't get the same nice, tight stitch with needles, don't know why) using proper knit and purl, which you can learn here (unfortunately I can't find my usual free source--sorry). If you can knit mittens or socks, you're a gall-dang superhero.
If you can't knit but your superpower is sewing, get some fleece and a pattern and make hats and scarves and mittens. I have this pattern and something like 5 yards of fleece waiting for me, and I love the hood and easy-looking mitten pattern. Also consider the amazing ugly quilt. If you can't sew but your superpower is shopping, I recommend buying up all the socks and underwear (for both men and women) you can get your mitts on. Again, check to see if your local shelter has a list of things they need and flex your shopping muscles on that.
General rules: Skew dark. Dark colors hide dirt better and therefore can go longer between washings. As charming as some yarn may be, I'm getting word that solid colors are preferred--if you're the creative knitter type, think of the project as meditative instead of creative and save your mad fair isle skillz for a nice sweater. I'm getting conflicting reports on wool vs. acrylic. Wool is warm, as we all know, but we probably also know what happens when you put wool in the washing machine on hot. Let's not even talk about the dryer. Naturally, my stash is flooded with wool yarn, so my hats and scarves are all wool. If you have the choice however (and maybe have the money to replace your entire yarn stash with acrylic), I'd skew towards the manmade fibers. SKEW LARGE--that's very important! Chris has a pumpkin-noggin, and if I can't get a hat I've made to fit on his head I know it's no good. If it can fit a man, there's a good chance it'll fit just about anyone who needs it.
In summary: Large, dark, solid, acrylic hats, scarves, mittens, and socks.
That's all I've got. Thanks for listening to me. I feel a little better. Happy knitting/sewing/shopping!