Flat design is web design trends nowadays. So, it is affect to all component of design. One of them is icons to use in web design. Here, i share 16+ flat icon sets to use in your design.  These icon sets divided into various topics that has its own uniqueness, because its designed by different people. I collect this from freebiesbug.com

Here they are..

1. 75 flat-style PSD icons

A set of 75 flat-style useful icons also provided in AI format. Free PSD designed and released by Adam Lindfors.
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2. 12 flat & coloured PSD icons

Here is a small set of 12 flat & coloured icons. Free PSD created and released by Yiğit Pınarbaşı.
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3. Roundicons – 60 free coloured icons

A set of 60 free coloured icons released for Smashing Magazine. It includes PNG, SVG, EPS, AI formats. Designed by the creative trio at Roundicons.
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4. Meroo Icons – 110 flat coloured PSD icons

Meroo Icons is a free set of 110 flat coloured icons created with Photoshop vector shapes. Free PSD released by Hesham Mohamed.
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5. 64 free PSD flat icons

Here is a set of 64 free vector flat icons in two different styles for bright and dark background. They are thoroughly drawn in 3 sizes (15×15, 30×30, 60×60 pixels). Free PSD released by Valery Zanimanski.
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6. Smallicons – 54 free icons

Smallicons is a set of 54 free coloured flat icons. The icons were made using Photoshop vector shapes and are available in different formats (SVG, PNG, PSD). Designed by Gimpo Studio (Nick & Oksana).
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7. Freebee Icons – 18 free icons

Here is the free icon set of Freebee app. It includes 18 coloured icons. Free PSD designed by Deividas Graužinis.
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8. 16 flat icons PSD

Here is a set of 16 flat and coloured icons that you can use for inspiration. Free PSD designed by Andrew McKay.
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9. Ballicons – 15 free PSD icons

Ballicons is an awesome set of 80 flat and coloured icons. Only 15 are free but we strongly suggest to spend few dollars if you need them. Free PSD designed by Gimpo Studio (Nick & Oksana).
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10. Random free icons AI

A set of 12 random coloured icons created with Adobe Illustrator. This freebie has been designed by Bogdan Rosu.
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11. Modern long shadow icons PSD

Today we have found a stunning long shadow icon set free for personal and commercial use. Free PSD designed by Ray Cheung.
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12. PSD Flat Social Icons

16 flat-style social icons in a free PSD. The icons follow the new trend of long shadows that make them pop from the background. Released by Pixeden.
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13. 12 flat SEO icons

Today’s freebie is a set of 12 flat SEO icons with long shadows. Free PSD designed by Vladislav Karpov.
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14. Flat Design Icons Vol4

Today Pixeden has released the Volume 4 of flat design icons set. A free awesome PSD that you can’t miss!
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15. Flatilicious – 48 Free Flat Icons

Here’s nice pack of 48 free flat icons! Flat design is perfect so we decided we make some nice flat icons. Designed by Lukas Jurik.
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16. Ballicons 2 vol. 2 – 30 free icons

A free set of 30 pixel-perfect colorful icons from the Ballicons 2 Vol.2 icon set by PixelBuddha and exclusively released for Codrops. Three formats available: PSD, SVG and PNG.
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That’s all.. Hope you like this collection!.