Laura Mercier are usually pretty good with samples.
I love the tinted moisturiser (I have the oil free one as I have oily skin) - it looks natural on, wears well and gives a light coverage.
Mac Face & Body could also be an option, but they don't give out samples. They are happy to put it on you if you want to test it.
It's light to medium coverage - it's a funny one as it starts out being quite watery but becomes a tad more creamy as you work it into the skin. The more you work it into the skin, the more coverage you get.
I really like it, but I find it needs to be set with powder (again as I have oily skin). It wears well and looks great on the skin.
Estee Lauder Double Wear Light is great - it's a light coverage foundation for oily/combination skin, lasts well and just looks great all day. It isn't too matte on the skin - on me, it just looks natural.
Diorskin Nude is great - it's light/medium coverage, wears well and looks awesome.
I'm not a massive fan of the BareMinerals BareSkin foundation - it settles in lines and drier bits of skin and doesn't wear well. The brush isn't that great either.
The new Laura Mercier foundation called smooth finish flawless fluide (or something like that) is nice, but I don't like how it gets cakey on my nose. It is supposedly great for combination and oily skin, is oil free, light coverage and wears well (just not on my nose).
Bobbi Brown's foundations didn't work that well for me - I found them too yellow, they oxidized and generally didn't wear well. The long lasting one looked awful - anything matte seems to look ridiculous on me after a short while.
I've used Clarins Everlasting foundation. The sample I got before buying was amazing, but when I bought the foundation, it oxidized on my skin, was too heavy and didn't wear well - I looked like a mess.
I personally isn't massively keen on buying foundations without having had a sample first. I do make exceptions but very rarely.
I generally apply the foundations with a Real Techniques Expert Face Brush or Buffing brush - I find that the way it is applied makes a massive difference.