Simple enough.

What are the best (or simply your favourite) tabletop boardgame/wargame mechanics that you've used in a game?

I'm a huge fan of White Wolf's Storyteller RPG system. It uses a D10 based 'successes' system, where you roll a number of D10s equal to one trait representing you innate ability, and another trait representing your training. (So, in weightlifting, you might roll two dice for your Strength, and four for your Athletics). Every 8+ is a 'success'; one success means you did okay, five means you did amazingly well. Tens 'explode' and allow you another roll (where another ten means another re-roll and so on).

It's a great system for almost anything that isn't combat, which has never really been a problem for the games I run. (In one five year campaign, gaming for five hours every Friday night, there was exactly one fight. My games don't really involve fighting all that much).

I also like 40Ks 'AP' system; I know a lot of people seem to prefer a modifier, but I remember playing with those back in the old Rogue Trader days, and all it meant in practise was that no-one got a save, ever. I like how the current AP rules make each special weapon so specifically tactical - there's a real difference between flamer, plasma and melta, for example. I'm of the opinion that more rules = slower, more boring games, so anything which streamlines play is always a good thing in my book.

What about other people? What game mechanics do you really like?