Some of the ideas have aspects of the ranger, the avenger, the swordmage, etc.
Some ideas:
Martial/Primal ... the 'archer' type. Mark on attacks. If the marked target makes an attack that doesn't include the marker, or if it ends it's turn farther away from the marker, immediate action attack. Give him some powers to pull the target closer. Some other control effects (the class would definitely be secondary controller) including entangling, knocking prone, and interupting opponent's attacks. Basically things like cover fire, discouraging enemies from going in a certain direction, etc. And then give them the abilty to use the bow as a quarterstaff in melee, and give so "bowstaff" attack powers in addition to som close blasts with arrows. Basically, they don't necessarily get engaged in melee, but when they do, they'll probably keep focussing on that one or end up provoking if they keep shooting at a ranged target.
Another idea is a more psionic/arcane class. Implement based, and they can have a mix of melee/close attacks to go along with ranged/area attacks. They'd likely have a close burst marking feature which can snag extra targets with levels, feats, power points, etc ... Probably a 'teleport you next to me' feature triggered off going after allies. This encourages them to engage you ... especially ranged attackers since attacking you stops them from ending up next to you, which is probably one of the few things they would really care about. For melee guys, they may not care as much ... if the option is engage you now, or a turn from now when you end up adjacent, they'll probably just attack your ally anyway. In that case, maybe when they get brought next to you there is another mini effect. Maybe they are also slowed/can't shift until EoNT (so at least attacking you directly they could shift away and charge someone else afterwards). The idea would likely be the class would be less sticky, but have a better way of getting the enemies back to them. I think this can actually be handled by a Ensnarement Swordmage already ... the only thing being that his aegis requires the enemy hit to be used, requires you be close to put the Aegis on in the first place, but other than that, sort of accomplishes the main thrust of this kind of character ... pulling someone next to him when they attack anyone but him. This is probably the best "anti-ranged enemy" ranged defender.