You can always email them an offer to my site and save yourself the headache.
But for real, I usually email my ex-members a nice deal like 6.95 for 30 days that rolls over to the regular membership price. This works pretty well. I know some people email their ex-members every week. But I do it a little less often than that, probably once a month. Since they're good paying customers I don't like to bug them too often, call me silly. Also when I mail them I give them an update about what's new on my site and sometimes send a couple pics.
And I do offer them other sites as well, sites that I think they'd be interested in.