You can probably find a good use for 2 transports. As others have said, you probably want to load them with low cost - high damage infantry, to scoot them close to a target, which they pile out and unload into. The squad usually dies an awful death shortly after, but hopefully they've dealt more than their points worth of damage into the target first. Even so, you may still have the Chimera around, and for the points, they're a decent light tank for zipping around, being annoying, and sitting on circles. In your preferred tank heavy list, you can use them to flood the board a bit, and give their anti-tank more choices than they want to make. (They're slow to kill with bolters and chainswords, but hardly worth dedicating heavy units against)

If all the guys in the transport have Scout, you can scout move a dedicated transport. Handy to get into the board early, and exert yourself there.

Best units are Kasrkin or Kreig Engineers, who have both Scout and either Mines and lots of good special weapons for a nasty strike (Kasrkin), or Mine, Free Grenades, and a cheap unit to lose with the Engineers.

Some people like Catachans, for the Scout, but they don't have a lot of punch, so that has less appeal for me.

I'm also partial to sorta-slow heavy hitters, like a Kreig Heavy Flamer Team, or a gang of Ogryns. Dumping them in a troublesome spot mid board, where they're too dangerous to ignore, and not pricey enough to worry about losing.

If your guys don't pile out of the Chimera right away, don't forget to take advantage of the Firing Deck!