Cool but the drones are so expensive 30 points for one are they worth it?
Dean
In my opinion, no. Some swear by the stealth suit marker team, which is a minimum sized squad of stealth suits, a markerlight and (usually) targeting array on the squad leader, and some marker drones. An alternative is to attach the marker drones to a crisis suit squad. You lose the squad-leader's markerlight and the stealth field, but you gain some wounds, a point of toughness, and some longer range weapons. That fixes one of the problems with the stealth marker team, which is that their main weapons rarely fire because they're trying to stay out of range to be protected by the stealth field. Unfortunately, every time I've tried using marker drones in any quantity the squad ends up being too expensive and there aren't enough points left for "real" units that actually do damage.
Markerlights are very hard to use effectively, which is a shame since they are a signature Tau weapon. Pathfinders are the classic way to get a decent quantity of them, and my favorite. They are by far the cheapest, even if you consider their mandatory devilfish wasted points (which I don't). But they are static and very easy to kill for as dangerous as they are. Against an opponent who's ever seen what they can do, they will almost certainly be dead by the end of turn 2.
In some cases, you can do well with a static gunline of multiple fire warrior teams, each one with a markerlight on the commander. It's a very static force and can be wiped out quickly by fast assault squads or heavy flamers, but it is a scary amount of small arms fire.
Sniper drone teams can also be markerlight sources, but I find they are too static and that they need the markerlight for their own use.
Finally, consider the skyray as a markerlight source. It doesn't do great if you only have one because it needs its own markerlights to fire its main weapon, but a pair of them can combine fire nicely. It will certainly surprise an opponent to see two skyrays on the field, if nothing else.
My favorite way of doing markerlights (other than not bothering with them and concentrating on regular weapons) is a full pathfinder squad and a skyray. In the first available shooting phase, pick a high-value target with a 3+ armor save or worse, and hit it with all 8 pathfinder markerlghts. Then move to the skyray, add it's 2 markerlight shots, and empty the missile rack on that target. Whatever that unit is, it's probably gone now, and the skyray has done its damage. The pathfinders will likely die now, but since the skyray has few if any missiles left your opponent is likely to ignore it, leaving it free to handle markerlight duties for the rest of the army.