Feral, retribution and enhancement are workable specs but I wouldn't recommend them to someone unless they know exactly what they're in for and specifically want to play that spec. Every raid should have room for one of every spec except prot paladins and elemental shamans, but if you aren't sure what you want, pick something more generic. Feral druids in particular have practically no raid itemization until AQ40.
If you intend to do a large amount of 5-man dungeons, also be aware that druids don't have a regular rez in vanilla so they're not quite optimal dungeon healers. It's completely doable but a bit of a hassle when people die as you can rez once every 30 minutes.
Most guilds are built on their tanks, so it's not usually the first thing they're recruiting. You only really need about three or four dedicated prot warriors (or even just a couple if you can guarantee 100% attendance from them) until Naxx 4H. What guilds end up needing is healers, mages and general ranged DPS in that order. Unless it's a completely new guild starting up, melee DPS spots are typically on an "exceptional players only" basis.
Since mage is pretty much the best DPS class in vanilla and you can never really have too many of them, that's a pretty safe bet. It's also just about the only DPS class that people actually look for in dungeon groups, so it's really easy to gear up a mage compared to the other DPS classes.
Druid: This may be controversial but i feel Druid are the best offtanks in this game. This is due to being able to fill other positions very well when not needing to tank. (with proper spec they could fill in as either dps or healer)
This is pretty much correct, although be aware that if going for the tank/healer spec (0/30/21 or 0/31/20), while you'll be able to fill two roles just fine, there will almost never be times where the raid wants to cut a healer in exchange for a tank or vice versa. You always swap healers and tanks for more DPS, nothing else really makes much sense. Any hybrid spec should have DPS as one of its hybrid parts, otherwise you're unlikely to ever get to utilize both. It's really nice for non-raiding dungeoneers, though.
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