I do most of my followup using my gmail and activeinbox. Maybe it sounds too simple, but you can schedule emails, make emails into a "to-do" list, and I'm able to keep track of everyone. Plus it syncs with my ipad and iphone (or any pad or phone.) My company (C21) offers drip campaigns, but you could easily use mailchimp for that. What I like, and I'm likely more simple-minded than many of the folks here (Top Producer and some others are way over my head - get me bogged down with too much info,) is that everything is in one place: my contacts, all of their information, their communication with me, anything I have scheduled with them, etc..

My 2 cents, anyway. Good luck!