Blogs are very amazing in exploring people's opinion and how they view things generally.
So, for my students I would highly recommend them to use it. I would give them some of the home-works to post it in their blogs which will be an open answer type of questions just so they will feel more confident and free in using the English language and their opinion.
Wiki, Oh wiki, I have a bad experience with this site and I don't really think its something our students in KSA are ready for it. But I have to say that it has some benefits. For example, I can give my students an online quiz so I could evaluate their progress. this is something for sure I would love to do in order to keep up with the class and not to leave anyone behind.
Delicious would be an AMAZING site. I would post them with good materials that are available online. direct them to video links that will help them in understanding some lessons. They will also be invited to share links that they might help their fellows in the class. Delicious will definitely be a helping tool outside the classroom to expose students to the language.