Far be it from me to try to convince you that you don't need to buy gifts for these people. By all means, get out there and do your part to stimulate the economy! Below is a list of suggestions (some of them locally-sourced and/or environmentally responsible!) for the most passive-aggressive gifting options I could think of. (Last year's version of this is here.)
1. Regretsy: Craft Fair Edition. This is the option that really has everything going for it -- it's locally sourced, the recipient can't return or exchange the thing you buy, and if you select your craft fair properly, you can find something for $10 that looks like you MIGHT have foolishly spent $30. Of course, there are many beautiful handmade things available at craft fairs, and you can buy from those artists when you're selecting gifts for the people whose company you cherish. If you pick your craft fair right (I hate to stereotype, but let me just suggest that the kind of craft fair you'll find in a church basement is more likely to have hand-crocheted Rudolph the Red-Nosed Reindeer hand towels than something like the No-Coast Craft-O-Rama -- though the No-Coast is more likely to have hand-crocheted Rudolph the Zombie Space Alien hand towels) you'll also have plenty of hideous items to choose from.
Think big! A small ugly knickknack can be easily hidden behind something else on a shelf. Maybe you can find a hand-tied fleece afghan in a print that will clash horribly with all this person's furniture. (Or pink camouflage. There's surely someone out there who likes pink camo -- I mean, I see it all over -- but it's always struck me as something that only the six-year-old daughter of an active-duty soldier would like.) Or a giant clay sculpture of God-only-knows-what glazed in mustard yellow. Or a sweatshirt with a festive multicolored snowman appliqued on the front.
Remember that beauty is in the eye of the beholder. Maybe you ARE at the No-Coast Craft-o-Rama (hurry, it's tomorrow) looking at the three-headed sock monkeys and thinking, "awww." But you are much cooler than your annoying relatives, and this might be just the thing to HAUNT THEIR DREAMS FOREVER.
2. Think cutesy! If the craft fair leaves you cold, you can browse through something like the Hallmark Store for wide-eyed china bunnies dressed as Santa. Try to find something that's too cute to callously discard, while nonetheless being useless clutter. If you find a gargantuan yet adorable stuffed animal, your shopping (for this person) is DONE.
3. If you're somewhere like Kohl's or Macy's or Target when you do your gift shopping, somewhere between the ties and the men's underwear there will be a series of shelves of random Masculine Gifts (tm) in little red boxes. Some of these gadgets are actually sort of neat (compact iPod speakers, which were all over one year but I haven't seen this year) and some might occasionally be useful (key fobs that beep when you whistle for them are The Thing this year, and who can't use another flashlight? okay, maybe not everyone has the Disappearing Flashlight problem that I have) but some are definitely in the WTF WOULD ANYONE NEED WITH THIS category (a talking tire gauge, in case you have to check your tire pressure in the dark?) and there is absolutely nothing that says, "I had to buy you a gift. So, here's a gift!" like a "desk puzzle" in a little red box for $9.99 from Kohl's.
4. If you're shopping for an ex, because the kids want to give him a present, focus on setting. If you take your kids to A Store, they will probably choose something from That Store. You might say to yourself, "I'll just take them to Target; I can get some other shopping done while I'm there," but recognize that you are wasting an opportunity. There are entire stores full of nothing but horrifying items: you probably don't want to go to the Thomas Kinkaide Store at the Mall of America (because if you're sensible, you don't want to go ANYWHERE NEAR the Mall of America in December) but take a careful look at the stores convenient to you. Is there a place that specializes in collectible plates with pictures of animals on them? Or a store that sells nothing but novelty socks? Or a Spencer Gifts? (NOTE: This is only a good strategy if your ex at least has the redeeming quality of being willing to pretend s/he just LOVES whatever the kids wound up picking out. If you have an ex that would hurt your kid's feelings over a Christmas gift, my suggestion for what this person should get for Christmas would potentially expose me to legal liability so I deleted it after typing it out. I'm sure you know a guy who knows a guy who could suggest the perfect
5. The Charitable Gift. This is where you give money to a charity and tell the person that you realized they are such an awesome individual that they'd rather feed the hungry than have new stuff. This can, in fact, be a perfectly fine and thoughtful gift. OR you can visit the Oxfam website, which allows you to give someone shit, worms, or crabs. (And if you search "coal," they have a suggestion for that, too.)
The great thing about this sort of gift is that if you make a gift in someone's honor, and tell the charity, "yes, please send them a card telling them all about the tribute gift," this will put them on the charity's mailing list and they'll be repeatedly badgered for more donations. (When I've given these, I try to be thoughtful and donate to a group the recipient already donates to. Which means I wind up on their mailing list forever and all time and they spend 5 times what I donated trying to get more money out of me, but that's a separate rant.)
For a passive-aggressive royal flush you want to pick out a charity that this person has never heard of, but would find somewhat objectionable if they fully investigated all the details. Bear in mind that if you tell your homophobic relative that you've donated in his honor to GLAAD, that isn't passive-aggressive but an in-your-face throwdown challenge; if you'll have to sit next to this person at Christmas Dinner you might want to find something more subtle. (Maybe. I guess it depends on how much confrontation you like with your turkey.) But for instance, you could donate in his honor to Avenues for Homeless Youth, which has some programs (like the GLBT Host Homes program) specifically to support teenagers who were kicked out by their parents because of their sexual orientation or gender identity.
Alternately, you can choose a charity that subtly critiques the person you're "honoring" -- a donation to the American Lung Association for a smoker, to Childhelp for a terrible parent, to ARC for someone who thinks "short bus" jokes are hilarious.
(PLEASE NOTE: I don't actually have to buy for anyone I dislike. And if you've ever given me a present and are wondering if I'm talking about you somehow, I'm not, don't worry. This came out of many message board conversations in which people groused about having to gift shop for their evil MIL, their impossible-to-please parents, etc.)