I must admit that vehicles play a very important role for me in 40k. This is a science fiction game, and vehicles are a key element in this setting for me. 4th ed will probably reduce vehicles largely in their effectiveness, but they should still be part of any 40k army in my opinion.

Predator Annihilator and Destructor

The predator variants are well armoured fire support units. While the annihilator is a tank hunter, the destructor is excellent against horde armies like orks and tyranids. The destructor's autocannon also serves well against lightly armoured vehicles like ork buggies and trukks as well as high toughness creatures. I always take sponsons and extra armour for extra fire power and survivability. 4th ed will give the predator more mobility, provided you take heavy bolter sponsons. In a mobile army like Black Templars this is a large plus. A very versatile support unit that is highly recommended.

Vidicator

The vindicator's demolisher cannon is devastating against every single unit in the game - provided you can get it into range. In 3rd ed this almost never happened, vindicators tended to be fire magnets. In 4th ed the ability to fire ordonance on the move will change this, which makes this fine tank a great option again.

Whirlwind

The whirlwind provides excellent anti infantry artillery. Most armies fear him, and rightly so. Despite of its effectiveness I rarley take one for my Black Templars for two reasons. The first reason is fluff - he's immobile and used to take out enemies at great distance. While one can argue that this fits the Black Templars' mother chapter, the Imperial Fists, excellently and thus fits into a Black Templars army, too, it doesn't fit into my view of their combat doctrines. The other reason is that I don't have enough heavy support slots. A predator, a vindicator and a crusader don't leave room for a whirlwind. And in larger games I might even want to take two crusaders, forcing me to drop the vindicator. This is very much a matter of taste, so don't refrain from taking this excellent piece of artillery if it suits your needs.

Land Raider

The mobile bunker. No vehicle is as impressive looking on the battle field except for an ork battle fortress, and the psychological effect alone is worth 250 points. On the other hand the heavy weapons reduce the land raider's mobility, and this won't change much with 4th ed. Furthermore a predator is almost as effective and costs much less points wise. Using a land raider as a transport alone on the other hand makes its heavy weapons a waste of points. If you take one, take him as a transport for your command squad in larger games and save your heavy support choices for other vehicles.

Land Raider Crusader

If there is a vehicle that screams "Black Templars" then it's the crusader. With a transport capability of 15 marines or 8 terminators and the ability to fire loads of anti infantry weaponry on the move, this is the perfect vehicle for any mobile and close combat orientated army. And Black Templars can take more than one of these beauties. Coupled with the psychological effect that every land raider's appearance on the battle field has, the crusader is worth every single point it costs. Granted, one lucky shot can take him out in turn one, and this happens about every fith game or so. But as long as you are aware of this fact and don't depend on the crusader, you're fine. In 1500 points games I almost always take a crusader in my Black Templars army, and I sometimes even take it in smaller games.