There are a number of bloggers who host regular weekly meme's and other's who host a one-off for a particular subject.
Let me give you an example:
Wordless Wednesday at 5 Minutes for Mom - here's a link to check out
Each person wanting to participate does a blog post keeping with the topic required, links it back to 5 minutes for mom's post and then adds their blog post link to the Mr. Linky. You can then check out the links of other participants.
You'll find that there are many MANY meme's going around the blogosphere that you can participate in ... for example Thursday Thirteen, Weekly Winners, Candid Carrie's Friday Foto Fiesta, Menu Plan Monday etc. Just jump right on in.
Then of course there are the meme's that float around the blogosphere from blog to blog. One person tags another with a questionnaire or to post something particular on their blog and then they tag so many people and around and around it goes. Personally I find these a pain in the neck and rarely end up participating because they take away from what I would rather post on my blog, but a lot of people love them as 'fill-in' posts for when they haven't got much to post about one day. However I do enjoy photo meme's. There was one that involved posting a certain photo from a picture folder on your hard-drive. It was funny to see the shots that people added. Then there was another where you had to take a photo of yourself that very minute and post it. That too was funny to see all the different responses. These are harder to get involved in unless you are tagged, but that's not to say that you can't start your own meme and send it to a few bloggers that you know and so forth. You will also find that a lot of bloggers don't like to just tag a few people, but will instead leave it open for everyone who reads their blog to participate. If you choose to participate, just make sure that you add a link back to the site you found the meme on.