I think as a kid it went walmart garbage, walmart garbage, Stingray, walmart garbage, walmart garbage, and walmart garbage. When I was 15, I was obsessed with cars and couldn't wait to get one. Right around 15 1/2 I found a '81 Schwinn Traveler at a garage sale for $5, and got hooked on bikes and totally forgot about a car. The Schwinn was way too big for me, and was eventually replaced by an equally large GT Timberline. I can't remember if there was anything between them and me ending up with a '01 Trek 8000 that was way too small and had a strange mix of cheap parts. I think I put about 500 mi on each of those before moving to the next.
Afterwards came a '95 GT Pantera, finally a bike that fit! Over time it gathered some interesting parts, including a Velomax wheelset that had almost the same MSRP as the rest of the bike. I think I had that for at least a year and a half (Longer than any other bike since first finding that Schwinn), then gave it to my boyfriend at the time for his birthday. At the same time I had that, I also had an Austrian-made Sears 3-speed, a 3-speed Schwinn Varsity Frankenbike, and a too large Centurion Ironman.
I think the first bike to replace the GT was a Trek Cruiseliner with a Nexus 8-speed hub. I can't remember at all what came next. Then I found a '95 Fuji Discovery that was amazing to ride, for some reason I thought it needed disc brakes, had the frame sent off to get a tab added, and haven't built it up yet. Next was a '93 Giant ATX 780, once the recalled fork was replaced it became one of the best riding bikes I have ever been on, and for some reason I sold it to a friend. Luckily, she wants a frame swap, so I get it back soon. Soon after getting the ATX, a trade-in showed up at work that I absolutely knew I had to get before I even had a chance to ride it. Since then, my Schwinn Mirada has been my main ride, and it's evolution is probably worthy of it's own thread.
Those are just the main ones that come to mind, there were a ton more bikes I flipped, or bought with the intention of keeping then flipped.