Today I had a BBQ and made this marinade from an epicurious.com recipe. I thought it was quite yummy and somewhat reminiscent of chimichurri. I'd make it again.
Put thyme, oregano, salt and garlic is a mini-chopper. Process until garlic is finely chopped. Add lemon juice and process until well mixed. Repeat with olive oil.
Marinade tri-tip in the sauce for at least 2 hours.