Hi Holly,
The only place I have an 'ad' listed per se is in the directory at
Virtual Assistantville (still have to add more info there, but the basics are up there

), and I have my site added to the directory here at VAF. I reply to RFPs from both of these if it is in one of my areas of expertise.
I network with groups I am interested in at LinkedIn. I have Google Alerts setup to send me a daily digest of my areas of interest - then I can check out the ones that peak my interest. Facebook...not so much, but plans are in the works for upping my presence there. I'm an infrequent Tweeter, but have gotten some one-off projects from there...hmmm...maybe I need to tweet more.
I have never used Craigslist because I wanted to find groups that are pertinent to what I do. I've gone the route of Elance, etc., but I didn't find them as helpful for finding work.
Some of my work comes from referrals. Some work from being a sub for other VAs. I think that these come because of establishing a presence here at VAF, which is such an added bonus of being here!
My biggest 'ad' is my website.
Three of the best things you can do are:
1) Network
2) Network
3) Network
HTH a bit,