I want to roll a new shaman and / or priest. I was wondering if anybody could give me link(s) to some good guides, webpages and resources around the web where I can find the best info about these classes. I like to roll a resto / ele shaman and a disciple / shadow priest.
I would suggest the threads here as a good starting point. I found the Holy Priest one to be very accurate. However, if you are starting a priest, then you should really do shadow until you are ready to raid anyway. Levelling will be much quicker.
PlusHeal.com has fantastic healing Priest boards, Shadowpriest.com is great for tanking (Sike! yeah it's for Shadow Priests), and TotemSpot.com is a pretty good Shaman site that's still getting off the ground.
That being said, I wouldn't worry too much about research until you reach Northrend or so. You will learn the basics just by healing or DPSing dungeons.
A few tips:
As Resto, always keep an eye on your Water Shield (once you get it that is). Letting it fall off for too long can lead to major mana issues, it really is important.
Low level healing is pretty straight forward - put Power Word: Shield on the tank, put Renew on him when he's taking damage, and top him off with Penance or one of your other direct heals.
Low level Resto - Earth Shield the tank, then use Healing Wave or Healing Surge to top him off. Again, very easy and straightforward - Earth Shield does most of the work for you at those levels.
Seek out gear with Intellect, Spirit, and Stamina (in that order more or less). Other stuff like Crit and Haste are nice where you can get them, but far from crucial until you get into 60's and 70's.