Art. Cheap artwork. Street vendor oils and watercolors. Especially of the cities wherever I happen to be. E-Z souvenirs and they look nice on the walls.
Our house is chock full of interesting stuff bought back from overseas- everything from cans of Coca-Cola from France to a small guitar from Mexico to an “Underground” plaque from London (a scaled-down version of the ones on the wall of Tube stations, made by the same people and sold by London Transport) to a radio from the US, to an Akubra hat from here in Australia… amongst other things gathered from the four corners of the globe!
I call it my “Collection of Interesting Things”. My Mum calls it “Crap you’ve carted back from the other side of the planet”. 
Earrings. Or cookbooks. Very occasionally, something to display. In Savannah, I got an aged-brass looking figurine of a man playing a French Horn; kind of abstract, and I loved it. But it has to be pretty cool to overcome the “If I have to dust it, I don’t want it” rule.
A pen/pencil that looks cute (e.g. the space-shuttle-shaped pencil from Kennedy Space Center). Or a Christmas ornament if I see one I like.
Not too costly, doesn’t take up too much space, and I can glance at the small item and remember the trip with pleasure.
CDs, lots and lots of CDs. I try and buy something local if I’m in another country.
I used to have a lot of other crap, but I don’t do that any more. It just costs money and I don’t do anything with it. At least with the CD I can listen to it.
I was working for a department of the state government and I realized that the others in the group took very nice vacations whenever possible so one year I suggested everyone bring home one truely tacky fridge magnet. We had a very ugly metal filing cabinet in the middle of the department but after a year, it was a sight to behold. The filing cabinet was no longer the Despised Thing and became a real showcase. I always collect magnets when I travel especially when I have one of those multiple connecting flight trips so I get 3 or 4 times as many magnets for one trip.
When in Florida we always pick up another flamingo thing and when I get to Montreal I treat myself to something wonderful from one (or more) of my favorite bath and body places like Lush, Bella Pella or Fruits & Passion. Everytime I use the Buddha Baby White Chocolate moisturizer I think of the tiny shop we stopped in.
I have a book problem while traveling. My suitcase always gets a “heavy” label smacked on it and there’s usually a surcharge.
I like wearing necklaces, so I try to always buy myself at least one new one I can use for everyday.
Except last year, on vacation in Ebeltoft, Denmark, with my three sisters-in-law, I got some beautiful glass crafts and a metric buttload of clothes. And no necklace. Truly these ladies are a corrupting influence.
Yeah, this is pretty much the way I roll. Experience culture through the local cuisine whenever I can. I even visit foreign grocery stores to see what the local like to buy and eat.
I often get books as souvenirs - just brought home a double volume of ‘myth-ing persons/little myth marker’ from montreal, and I got my copy of ‘the princess bride’ and a novelization of ‘spiderman’ in Kingston - and maybe a third book.
Yeah, I could get these books closer to home or order them online, but this way when I read, I’m reminded of the trip - as long as I can keep straight what I bought where and when 
Like Antigen, I always buy a Christmas ornament or something that can be made into an ornament. I’ll bet I have the only tree in town with a armadillo on it. So far I have always found something I can use everywhere I 've traveled. Family members bring me stuff from their travels, too, which is nice.
Refrigerator magnets and shot glasses. I also love trying the food when traveling, and will often bring candy home for friends. And I come from a family with a long tradition of collecting knick-knacks. I love little tiny sculptures, carved wooden boxes, candleholders, etc.
I likely to visit museums and museum gift shops. They have great stuff to take home as souvenirs. Whether it’s there, or elsewhere, I generally look for art or handcrafted objects. I have a thing for wooden boxes, and own quite a few of them, inlcuding a couple of puzzle boxes I also like jewellry, which I generally buy watches, necklaces or bracelets. The nice thing about jewellry is how little space it takes up in the suitcase or carry-on, and I get wearable memories.
Blowjobs. Usually in 3rd-world countries they are much cheaper.
When I go to England (as I will be again later this month), I bring back tea. I look for interesting blends and collect interesting tins, and also wander the cluttered little antique shops looking for old-fashioned tea toys, like unusual sugar tongs or strainers.
A bit of silver jewelry, perhaps. I don’t buy stuff when I travel very much. I travel too much and dont’ have a tchotchka jones.
I bring home a number of things mentioned above - including christmast ornaments and cook books (even in foreign countries there is often an English section in book stores of local cuisine).
But like the OP, when I was doing a lot of travel in Europe I tried to get things of use:
A wool blanket and mittens in Norway
Shoes and earrings in Holland
Crystal vase in Prague
A woodcut and oil/vinegar bottles in Poland
A cheese grater and La Perla in Rome
A painted plate and tea glasses in Turkey
Jimmy Choos in London
An ornamental hair comb from Seville
A fantastic lamp from Fez (genie not included!)
And the OP is right - each time I use them, I get a flashback to my travels, which is great.
I have a book problem while travelling as well. So far I’ve managed to avoid the surcharges, but, one day …
As already mentioned as well here, I visit museum gift shops too. Between that and the Second-hand Bookstore Menace, I’m doomed unless my will is strong (it usually isn’t). 
I haven’t traveled much, but here’s my inventory.
On a trip to St. Lucia, I brought back an onyx chess set and two bottles of hot sauce (I called them volcano sauces).
On a trip to Mexico I brought back a malachite ring and a turquoise chess set.
On a trip to London I brought back a set of tea tins and a mug with a dragon on it.
The next trip will be to Florence, and there’s a painting of a woman in a veil I’d like to bring back, but I doubt I can manage that.
T Shirts and pins. When my sister visited England with her husband, she asked what I wanted. I told her I wanted coins, or tokens from the Underground. I think money in coin form is cool, and you always know where it came from.