[Rufio]

Odeseus,
Many guilds you can look at if you just want to go on some raids. Anonymous as Loramin mentioned above, Blood Guard, The Second Sons, Venerate, Kittens and a few others do some raids during the week and weekend. They also try to target much of the Kunark/Old world bosses on repops/quakes with some velious targets.
If you are looking at ToV targets, I would say Paradigm Shift, Azure Guard (guild I am in). Most of the guilds listed do Sky on some day of the week, along with HoT. All of the guilds listed are capable of down much of the raid content but are more opportunity oriented.
P.S. Check the front page of each of these guilds forum post to really get a feel for them. And most guilds won't have a problem with you tagging along, so you can get a feel for their style.