The first thing to do is not to drop your insurance because you had a DUI. That's an invitation to open yourself up to even more trouble down the road. A DUI on your record is bad, but a DUI with an insurance lapse is even worse. At this point your focus should be on rehabilitation, both for yourself and your driving record.
A DUI is not the end of the world when it comes to auto insurance. While you're not likely to qualify for a standard or preferred company, there are carriers that target drivers with problems on their driving record, up to and including multiple DUIs. Premiums for some of these companies can be surprisingly reasonable. Most insurance agents have access to at least one of these companies, so in many cases you won't have to change agents.
In the event your agent isn't appointed with a good non-standard company suited to your particular situation, chances are he knows someone who is. Don't be afraid to ask for a referral.
While it's possible to purchase insurance online with a DUI or other serious offense on your record, I don't recommend it. Your local agent is likely better-equipped to find the most cost-effective solution for you.
A good agent will also keep tabs on your record through periodic reviews and make sure you're moved into a less expensive company and/or rating class when you qualify. While a company could theoretically move you automatically, there's no guarantee it will. Active monitoring of your record as it improves over time is the best way to make sure you're consistently rated correctly, and working a live agent is the best way to make sure that happens. A web site can't provide that level of service, regardless of how cute the mascot is.
Look for any discounts your agent can offer. Package discounts for having your auto insurance with the same company as your homeowners, renters, business or even life insurance may still be available to you despite your record. Try to lock in as many discounts as you can.
If even the best quote comes back too expensive for you, you may be able to lower liability limits or raise deductibles to lower the overall premium. While it's never a good idea to lower your coverage below levels you're comfortable with, it may be an option to cut costs. Even so, I would do this only as a last resort.
Finally remember most insurance companies don't rate for any incident that occured more than five years ago, no matter how serious. As long as no further driving offenses are committed, it's possible even for drivers with the worst records imaginable to eventually attain or re-attain a preferred status with no tickets and no claims. Do whatever it takes to get yourself clean, and in time your insurance history will follow suit.