Well, I've been with them for almost 10 years now, and I am very happy with what I get every year:
1) Great value for what I pay - shell access, unlimited domains and subdomains, and unlimited users - that is pretty rare for hosts at this price level.
2) An ever-increasing bandwidth and storage quota (not that I am likely to use even what comes with the basic plan).
3) Friendly and professional support service, though I rarely need it.
There are a couple of ways that come to mind immediately:
1) Participate in the "rewards" program and make some referrals - three or four ought to cover your entire hosting charges for the next year.
2) Sign up for 10 years and get preferred pricing - though you will have to pay for the 10 years all at once, so you will spend a LOT more money now