There are so many great ones to choose from. It all depends on how much you are willing to spend. On the expensive side you can choose LancomeTient Idole Ultra 24 , that has already been mentioned. You can choose BareMinerals (which is one of my favorites) You can also go less expensive and purchase from the BOOTS line. they have a great line of skin care for oily skin and offer a variety of foundations such as tinted moisturizers and their Botanics Complexion Refining Foundation.

It also helps to use the right moisturizer and mattifying products :) Murad makes a mattifying moisturizer, and Urban Decay also makes De-Slick products that work really well with oily skin types.

During the summer, I use Bare Minerals Matte Foundation, but now I'm curious to try the Lancome one!

Matte, light,sheer and oil free or a powder finish. A little goes a long way and be sure to wash it all off every night before bed.

I completely agree with @Akitans26 about the Lancome Tient Idole Ultra 24.....I just tried a sample of it at Sephora, (my skin is not super oily but I wanted to give it a try). It was great and stayed on all day. Nice, matte finish to help keep the shine away. Another option is BareMinerals and Maybelline Super Stay.

LANCOME has a new 24 hour wear foundation...its non comeogenic, oil free, light but full coverage. As a person with oily skin its the only foundation that I can wear that lasts all day and i dont need to blot anymore during the day. Its great Tient Idole Ultra 24, also lancome often has free gift with purchases over 35 the prices for the makeup is 44. I also used it on teenagers for prom.

www.bareminerals.com
Powdered mineral foundation will absorb sweat & oils, so your skin will stay dry & look beautiful. If you prefer a liquid, look for a water based tinted moisturizer or foundation.

When my skin is oilier in the summer, I don't typically use foundation, just concealer. But if you need some coverage, try a light, mineral foundation or a very light cream base - like a cream to powder.