When you say roast, I assume you mean chicken?.....well, here are some ideas for chicken.....
You could rub herbes de provence into the skin, this is a dry mix of several herbs including basil, bay leaf, lavender, marjoram, orange peel, rosemary and thyme. This would be great if you are doing a 'dry' roast.
Slices of garlic inserted into holes in the skin is what I usually do. I put a sliced lemon inside the bird to keep the whole thing moist.
For a more exotic taste you could pierce a few whole cloves into the skin or place a couple of star anise inside (goes well with sliced oranges inside the bird and spoonful of orange marmalade in the gravy). Poivrons Vert or Rose (Green or Pink peppercorns can add a delicate flavor too)
The most wonderful aroma comes from a woody herb such as fresh thyme or rosemary laid inside and over the skin in whole sprigs, if you can find lemon thyme this will go beautifully with a whole lemon inside the fowl. If you wrap the whole thing before cooking the flavours will intensify. Tarragon is another classic poultry herb, again in whole sprigs laid over the chicken. My mother used to cook chicken with lovage - called Ache de Montagne here in the Alps, if you can find handfuls of it to stuff the chicken with, it will impart a wonderful celerish taste to the meat and gravy.
A good rub of celtic sea salt crisps up the skin too.
I sometimes use apple slices and cinnamon, sounds weird but it is delicious and if you combine that with cider (a cupful or two splashed over the bird before cooking) this really gets the aromas going.
You can also pack hay around the chicken, it keeps it incredibly moist - before you put it into the slow cooker, slather the chicken with fat and the herbs you have chosen, lay a bed of hay in the crock pot, nestle the bird in the hay and cover again with more hay. Make sure if this goes in the oven that no hay is protruding from the lid of the pot as this will catch fire. Cook on a low heat and make sure to let the bird rest for 20 minutes in the hay after you bring it out of the oven/slow cooker. The hay will have charred against the chicken, just scrap it off and carve the bird in the usual way. Here is a recipe that uses hay and pastry, but you do not eat the pastry, it is used to seal in the aromas of the cooked chicken. If the hay is sweet and grassy it gives the chicken the most amazing 'meadowy' aroma......you can buy hay at the pet shop.
bon apetit, let us know what you decide to roast and if it is beef, well, I can offer more suggestions!!