I'm a sucker for a traditional rosemary garlic marinade for leg of lamb.
Chop up a good handful of fresh rosemary. Mash about 6-10 cloves of garlic to a paste. Add 1 or 2 TB salt, 1 TB pepper, and stir around 1/4 cup olive oil to the mix. Spread it all over the leg, let it sit overnight and then grill the next day. Not original, but really, really good.
marinate in garlic, lemon juice and oregano overnight.
While on the grill, continue to base with the marinate. (I use a long sprig of rosemary to apply the marinade, like a brush.. I find this gives just the right amount of rosemary flavour... if you actually marinade it in rosemary, I find the taste too strong and can overpower the lamb)
Serve with a fetta and spinach salad
I marinate mine, pounded to even thickness, in a bottle of decent red wine, seasoned with salt, pepper, olive oil, a few cloves garlic, and sliced onion, for 8 hours or so. A recipe along these lines appeared in Gourmet in the 1980s and I have made my grilled lamb, cooked medium rare, this way ever since. A little fresh thyme is a nice addition.
These days for me it's a marinade with turkish spices featured in both Sortun's Spice and Wolfert's Eastern Med cookbooks.
The marinade for 3lb of butterflied leg is 2tbs aleppo pepper, 2tbs baharat (Kalustyans), 1/2 tbs dried crushed mint, 1/2tbs dried chrushed oregano, 1/4 cup of good tomato paste, 2tbs of red pepper paste (i usually used piquillo peppers minced to a paste), 1tbs of minced garlic. Spread over the meat, then cover with 1/4 good canola oil, and leave aside in cool place up to 4 hours.
We usually grill this for 3mins on each side to char a bit, and then cover and do indirect grilling for 10-15mins more.
not a marinade but more of a wet rub:
3-4 cloves garlic minced with
2 tsp kosher salt
Add 2-3 T minced fresh rosemary leaves
1 T fresh ground peppercorns
1 1/2 tsp allspice
3-4 T olive oil
Mix and rub onto lamb as it sits on the counter to come to room temp before grilling.
adapted form a Julia Child recipe for pork loin.