Zombeavers is amazingly awful 
I've seen The Langoliers too, actually I've seen it twice, but I still couldn't tell you what it's actually about.
Joy Ride, which features a psychotic, horny trucker called Rusty Nail. Also features Paul Walker though, so worth watching just for him.
Piranha - terrible but hilarious.
Agree with Battleship, San Andreas and all of the Sharknados. I've seen Bait, the sharks in the supermarket one mentioned above, it's definitely in the same category, as are Surrounded, Darktide, 47 Metres Down: Uncaged and The Meg.
Snakes On A Plane, Baywatch and Deep Blue Sea aren't bad-but-good, they're just good
As is Lake Placid, I love that movie.