Which is the best Heatsink for the 2600K (not overclocking) in terms for Silent, and Cooling?

Lots of good choices. Depends on your needs for size and price.

If you have a big case, I like the Megahalems because of its simple and effective mounting system, paired with a quiet 120mm PWM fan.

Reputable brands for making CPU heatsinks at SPCR: Thermalright, Noctua, Scythe, Prolimatech. I guess "best" heatsink in terms of quietness is thermal performance at a certain noise level. Currently, many heatsinks offer comparable performance. Just take a look at some of the latest reviews.

BUT! a 2600k at stock speed really doesn't run that hot. You can easily keep it cool without using some of the heaviest & biggest heatsinks which can weigh more than 1 kg! For quietness, you should focus on the fan since the difference between the best heatsink and an adequate heatsink with the same fan may only be 5 degrees celsius. Take a look at this page for example:

http://www.silentpcreview.com/article1171-page6.html

The temp increase for Thermalright Ultra-120 eXtreme Rev.C is 43 C, while it's 48 C for the budget Cooler Master Hyper 212+.

A good advice would be to buy a good heatsink which is bundled to a good stock fan. That way, you don't have to look for aftermarked fans.

Would a fanless HR-02, be sufficient for a 2600K(non overclocked)?

This build looks susccesful with a HR-02 passively cooled 2600K.

Sure, an HR-02 with a case fan nearby will cool a stock 2600K. But why would you spend so much on an unlocked CPU and not at least moderately overclock? 40-42x clocking doesn't even need voltage or cooling adjustment...

2600, 2600K, all the same to me.

I will buy the 2600, and save the $30 (which will go towards my heatsink).