In the end, it really depends on what your budget is, AND how often you think you'll be using a shotgun for deer hunting.

If you can shell out $300-350 (or less if not already scoped), you can pick up an H&R Ultra Slug single shot in 12 or 20 ga. I hear they are tack drivers and can't be beat for the money. Here is a link to some for sale at Gunbroker: http://www.gunbroker.com/Auction/SearchResults.aspx

If you don't like the idea of having a single shot and want to spend more, I really like the Savage 212 or 220 F. They are both bolt action slug guns.

If it's something you are gonna use regularly or at least annually, I really like the idea of a dedicated slug gun. HOWEVER, I do not agree that it is the only way to go, especially if you're not going to be using a shotgun for deer often...or ever again. And I also do not agree that there isn't a place for buckshot. I'll explain as I relate my experience with my Remington 870 (Express ) with its 28" smoothbore.

With the standard Remington chokes, my patterns with Remington buckshot were awful. I'd probably get 2-3 pellets in the 10-inch circle I was aiming for at 50 yards. With rifled slugs, I was hitting high about 8-10 inches and left about 4 inches and at 100 yards I couldn't even hit paper (COMPLETELY unusable in the field). Now, granted I was very new to guns at the time and didn't try a variety of buckshot and rifled slugs in my gun to see what worked best (costs a few bucks to do also!!). But, in retrospect, with patterns and accuracy that poor, I don't know if there would have been a magic load that would have cured the issue.

But I decided to try one of those "magic chokes" instead. I ordered a Wad Wizard (google it...I don't think we're allowed to post links to commercial sites but I may be confused with another forum's rules) and decided to give that a whirl. Lo and behold, using the same cheapo rifled slugs, I was hitting an inch high and an inch left at 50 yards, with holes touching just about every time (using just a front bead...no rifle sights). Using the same buckshot, I put 7 pellets in a 10-inch circle at 50 yards. Both completely usable in the field.

So, if you're on a budget, I'd take your Benelli out as is, use a modified choke, and try a few types of buckshot and a few types of slugs (some of the ones suggested by the other posters in this thread) and see how she does. If the gun doesn't perform well, I'd say it was time to look into an alternate choke, an alternate barrel (not really a good option IMO...you can buy a whole gun for just a little more than an aftermarket rifled barrel), or look into a slug gun. Of course, if it were me, I'd just buy a muzzleloader (assuming they are legal where you are going to hunt...MOST areas that allow shotguns also allow muzzleloaders). That way you can hit the muzzleloader only seasons that you'll miss with a shotgun.

Almost forgot...back to buckshot, it has its place. I have hunted with it a grand total of one day, and killed three deer with it, all who died quickly. It is excellent for still hunting (where you might jump a deer) or hunting in thicker areas where your shots are never going to be more than 40 yards.