On the subject of roasts, one of my favorite pieces of meat to roast is lamb. In response to Louisa's questions about lamb, you don't buy a whole lamb (although I suppose you could, if you felt inclined to take up butchering). You generally buy a leg of lamb, which is a big hunk of lamb meat that often comes boneless, or a rack of lamb, which is the ribs of the lamb. Or you can buy lamb chops, but you probably wouldn't roast those.
A rack of lamb is often rather expensive, but a leg of lamb on the smallish side can be reasonable and well worth the price.
Here's a classic version that's simple and I can vouch for how good it is:
Leg of Lamb with Garlic and Rosemary
Makes 8 servings
1 (7lb) semiboneless leg of lamb, fat trimmed to 1/4 inch thick
4 garlic cloves
1 tablespoon sea salt or kosher salt
2 tablespoons chopped fresh rosemary
1/2 teaspoon black pepper
1/4 cup dry red wine or beef broth
1. Preheat oven to 350 F.
2. Pat lamb dry and score fat by making shallow cuts all over with tip of a sharp small knife.
3. Pound garlic to a paste with sea salt using a mortar and pestle (or mince and mash with a heavy knife) and stir together with rosemary and pepper. Put lamb in a lightly oiled roasting pan, then rub paste all over lamb.
4. Roast lamb in middle of oven until an instant read thermometer inserted 2 in. into the thickest part of the meat (do not touch bone) registers 130 F, 1 1/2 to 1 3/4 hours. Transfer to cutting board and let stand 15-25 minutes (internal temperature will rise to 140 F for medium rare).
5. Add wine to roasting pan and deglaze by boiling over moderately high heat, stirring and scraping up brown bits, 1 minute. Season pan juices with salt and pepper and serve with lamb.
Since you're likely to have extra rosemary, buy some vegetables - onions, butternut squash, bell peppers, potatoes, beets, carrots, or whatever you like - roughly chop them up, toss them with some olive oil, salt, pepper, and rosemary, put into a shallow pan, throw in a few whole rosemary stalks and roast along with the lamb. You can probably put the veggies in the oven when the lamb has roughly a 1/2 hour to go. Depending on how many veggies you have, it shouldn't take more than 45 minutes. Then get some good bread and make a salad and you have yourself an amazing and simple meal that can also be for a lot of people (like if you want to invite me over...).
Here are a few fancier recipes to try if you give roasting lamb a go:
(Disclaimer: I haven't tried any of these, but they are all on my list of recipes to give a try and some only require a few ingredients.)