One of the first questions that one needs to look at when decided on gem would be are you a bonus gemmer or not? What I mean is do you match color slots or not? Are the +7 bonuses better then putting a higher value gem?
For example: a red socket can have a red gem, orange gem or a purple gem placed in it and still receive the socket bonus. However if I put in a blue gem, I will not get the bonus.
I am a person who does not really care if I match gem slots to get bonuses. If I happen to get the bonus, great! If not, well it is really no big deal. But you will find some people out there that think the bonus is everything.
Really, there are only a few gems that a resto druid should be using. Spell Power and (if you are not hasted capped) Haste. The Spell Power gem is called Runed Cardinal Ruby. This is a +23 Spell Power gem and this will surly trump any +7 or +8 bonus you can get using any other gem.
The Spell Power/Haste gem you can use is called Reckless Ametrine. This gives the wearer +12 Spell Power and +10 Haste. Using these will hepl you reach your haste cap and you will match yellow and red sockets.
As for meta sockets, there are two that can benefit a resto druid, but one that I greatly favor. I prefer the Ember Skyflare Diamond. This gives you +23 Spell Power and %2 Intellect for only 3 red gems. And if you gem Spell Power, then you will have no trouble meeting this meta.
Another meta is called Insightful Earthsiege Diamond +21 Intellect and chance to return mana on spell cast. This takes one of each gem (blue, yellow, and red). You will need to gem at least one haste gem with this meta and you will need to get a blue gem. My recommendation is Purified Dreadstone. This is a +12 Spell Power and +10 Spirit gem. Again I would only do this if I needed to make the socket.
Basically Runed Cardinal Ruby =good. They will get you the most bang for your buck!