I've had 4 that were shockingly good for the price, or the expectation.
Another vote for Opinel- I got one for a couple bucks in some country or another as a simple dungarees utility knife for nasty work parties, a 4 inchish one. That thing lasted until I gave it to a boot saving my ass on the flight line. Still going strong, probably.
My Meula Ranger, which I bought in Spain and took all over the middle east. I figured it was another one of the touristy spanish steel things at the time, and hell, they are dirt cheap in country. But I need *something* right then and there and it was what I could get (and I had my SAK anyhow). Stronger and more durable than it has any right to be. I got bored during a month of 12 on 12 off watches in the middle of Nowhere, Saudi Arabia and put more serrations on it, then made them sharp. Worth doing.
Number 3 is the Gerber AR I got 5 years or so ago on super big5 clearance for like $20. I was going on a trip and didn't want to take anything worthwhile. Once I remoiled it, it got lightning fast, it stays sharp better than I expected, and it's now in the pocket of a female friend who needed a decent light utility knife and wanted a tactical side. Sharp, smooth,and simple.
And- not that this was a HUGE surprise, but my most recent SAK is a lockblade Outrider. I know what to expect from the can opener, screwdrivers, and such. But the blade holds up better in my work than I expected (and I've abused it, even cutting low voltage wire when I have to) and the saw turned out to be usable enough that I don't run off to my bucket for a pruning saw for small stuff. I know they're good, I've been sarrying Victorinox since I was in the cub scouts, but this one is a bit more useful and durable than I had expected.