Do you have a grill currently? What is your price point?
There are a lot of things that qualify as a "smoker". Generally they fall into categories, which I'll summarize below.
My guess is if you really want a smoker/grill combo, a kamado-style or a Pellet grill are your best bets. They're the most versatile single use type grills. But if you already have a grill and just want a dedicated smoker, you have a lot more freedom in your choice.
Electric/Propane smoker: Usually these are not well suited for grilling. They could be used for roasting, if you can get them up to 350 degrees or so, but not really ideal for grilling.
Charcoal or stick-burner offset smoker: Not made for grilling, at least if the fire is in the firebox. Some are designed to allow you to also build a fire under the grate, and in this case it would be completely useful as a grill. Again, like an electric or propane, if you could get the temp up, they'd also be pretty decent for roasting.
Weber Smoky Mountain / Ugly Drum Smoker / Pit Barrel Cooker: Any of these "bullet" or "drum" smokers *could* function as a grill. It wouldn't be ideal, just based on the shape and access, but you could do it.
Big Green Egg / Char-Griller Akorn / Kamado grill: In a lot of ways, these are even more grill than smoker, but they do it all. They're completely functional grills, and they're smokers.
Pellet Grills: Again, these are fully functional grills and fully functional smokers.
The old-school Weber kettle: This is primarily a grill. There are ways to buy adapters and other things to smoke in it, and it can use that. But it's primarily a grill and only secondarily a smoker.
Propane Grill: Again, this is primarily a grill, but you can do things like light one burner on one side along with smoking trays or wood inside foil packs, and use it as a smoker.
