I need to get black and white postcards printed (photo on the front, text on the back)—any recommendations?
Do you want genuine photographic post cards or Litho prints.
Also are you in Germany ? or somewhere else.
I've had good luck some years ago with Modern and more recently with VistaPrint.
"Vocation to Solitude -- To deliver oneself up, to hand oneself over, entrust oneself completely to the silence of a wide landscape of woods and hills, or sea, or desert; to sit still while the sun comes up over the land and fills its silences with light." Thomas Merton
As Kirk wrote, Modern Postcard has been good.
ABC Picture or Postcard, I believe in Arkansas
Real photographs are born wet !
Most 4x6" photo paper falls within the USPS specifications for postcards. Text can be printed on the back with many laser printers, and the photo then printed on the front.
I use an Epson 4800 printer with Moab dual side rag inkjet paper. I print 6 up flip the sheet and print the post card on the back. It is limited production but is very effective with high quality.
If you want more than ~1000 of 6 cards, then conventional litho, doing either four-color or old-but-wonderful duotones is competitive with the online digital presses.... but it's out of sight if you need less than that.
For online digital, 50 to 500 of 1 cards, Moo.com is more expensive than VistaPrint but their quality has been good.
But for really short runs, under 100, an inkjet is better quality than anything short of a darkroom print. And probably cheaper.
It's hard to feed a 4x6 through your inkjet and get nice gripping and small margins, but every printer/driver/paper is different, let me know if you ever find a foolproof great one ;-)
Also, the "bulky" "photo-weight" 300-gsm inkjet papers feel a bit on the wimpy side to mail. But I have mailed even Harman FB-Gloss AI cut to card size and it holds up fine, so most of the double-sided uncoated papers should be OK. In this case, the smaller 3.5-4 x 5.5-6-inch (close to the minimum p-card size) is beneficial for not flopping around as much as a larger size card. If you use mailing labels maybe you can avoid needing to print on the reverse side, since it tends to be a PITA and can cause a lot of extra wastage. If you do decide to try to inkjet print both sides, be prepared to dick around and blow a few. Also the thicker papers have their own quirks with feeding, setting, curling....