In the winter my highlighter of choice tends to be my The Balm Mary Lou Manizer because it has a slightly whiter glow to it, but as soon as the sun comes out I sway towards my more goldy tones.
For a subtle, day time glow I highly recommend Kevin Aucoin Celestial Powder in Candle Light. When I was trying to buy this it took me literally months to track down from Space NK, but I think it's pretty readily available now. When on the skin, it's the whiter of the bunch and the most subtle but adds a lovely subtle glow. (It looks a lot more beigey in the picture below than in real life).
The Kevin Aucoin Celestial Skin Liquid Lighting in Candlelight (same as above but in liquid form) is much glower than the previous one so is better for a more tanned skin and can be layered dependant on how statement you want your makeup to be. (I also love using this under foundation or tinted moisturiser for a more glowy/dewy look.)
I've also included the Becca Shimmering Skin Perfecter in Opal (liquid version) as an alternative - my bottle I got in a gift with purchase from Space NK and both are great.
In the below picture the only products on my skin are the Kevyn Aucoin Celestial Bronzing Vail in Tropical Days and a mixture of the above 2 liquid highlighters. I. Love. It.
Let me know what you think and if you have any faves I don't know about!