Ahhh, a difficult question, with no real answer. Microstock is just the selling of the images to a company. the TYPE of images you create are completely upto you. And the lens you need is directly related to the type of images you plan to make.
For example, lets say you desire to shoot nature footage and photos for microstock because you love hiking and nature and own a nature reserve or live near the forest. You would have very different needs from a microstock photographer wanting to submit food photography, created in his studio. Because what you specifically want to shoot makes the subject matter vary, it is an impossible question without knowing what you, the reader, specifically wants to shoot.
What we can do is go over the lenses from each category, in a rough over-view. First, we'll divide lens types into 2 categories: Studio/Travel. Studio involved prepared shots, in prepared light, with controlled environments. Where as travel involves outdoor photography in exotic locations.
Also keep in mind that this is a list of the creme' of the creme' so to speak. This list is not cheap, this list is not easy to come by, this list is for a serious photographer, it's expensive, but it has some of the best glass that is still consumer grade.
For close up food photography and/or Macro photography, there are 2 lenses that are spoken of repeatedly!
Tamron 90mm/2.8 Macro : A very sharp lens especially at the price point, with image stabilization to boot. Useful in food and macro photography since it is sharp in the middle and a 1:1 magnification with a Fstop of 2.8 for very shallow DOF when desired.
Canon 100mm/2.8L IS or Canon 100mm/2.8 non-IS : Both offer amazing optics, the difference being IS (Image Stabilization) and about 500$. You cant go wrong with either one really.
Note that both of these lenses can also be used for portraits, but its really in the Macro world where they shine.
There are a few lenses here that are "staples" of this area of photography, including a telezoom that some may have overlooked for "studio" work.
First, I'll mention that a Prime lens is amazing in a controlled environment. As such, we'll discuss the 50mm 1.8
Canon EF 50mm f/1.8 : This bad boy is one lens that I recommend EVERYONE get, it's cheap cheap cheap and allows for a very shallow DoF when wide open. It is not sharp when fully open, but stopped down to 2.8 or so and it becomes a fairly competent lens with many options! Not a zoom, this will require your feet to "zoom" in and out, because it is a prime lens.
Next we'll discuss the Canon EF 24-70mm f/2.8L:This lens is considered to be a great studio lens for many reasons. It is sharp as a razor and has great contrast. It's "downfall" if you will is no IS, in reality though, it may not be a necessary thing to have for *most* studio setups, since your model and "lifestyle" shoots dont usually have your models swinging through the air, nor running 30 yard sprints.
Lastly, I'd like to mention the 70-200mm Canon f/2.8 IS ii Telephoto: This lens is amazing in contrast and background compression. It is used very often for headshots and for outdoors work for its ability to compress the background and create a creamy texture despite being at a "stopped down" f-stop. The lens provides very acceptable images at f/2.8 though and will be a God send in a low light shooting environment where distance is unchangeable.
TRAVEL: Walking Lens
A walking lens is basically a lens that is acceptable for a wide range of applications and uses, with little compromise to Image Quality. There is one favorite in this category. The Canon 24-105mm f/4L IS is a great lens with an acceptable and convenient zoom length. It includes IS for necessary moments and low light shooting and has great image quality!
TRAVEL: Wide Angle Lens
Landscapes and panoramas your thing? You want to take an HDR of the swiss alps? Maybe a panorama of the grand canyon? You'll need a wide angle lens (or want one, at any rate) to take in as much of the scene as you can. You can go fish-eye (but the distortion is significant), but sticking no distortion free we have one clear winner that even topples the Canon version, in my book. The Tokina 11-16mm f/2.8 ATX lens. The lens is superior to the Canon version, in that it has a 2.8 aperature throughout the whole range, where as the Canon version is 3.5-5.0fstops. This lens can go from wide to slightly less wide, to accommodate both Crop sensor and Full Frame Cameras. Great sharpness and contrast, a must for the landscape aficionado!
TRAVEL: Wildlife Lens
This area is for the stock photographer interested in Lions, Tigers, and Bears (Oh My!). The same lens I mentioned above, the 70-200mm Canon f/2.8 IS ii Telephoto is where you want to be here. Yes there is a 300mm lens... yes it has good optics *(not the 75-300mm f/3.5-5, those optics are fairly bad!)*, but the cost is very high on the 300mm good telephoto. A better option here is to add a Canon EF 1.4x iii Extender. It adds length to your lens at a very small quality cost. A 2.0X version exists, but it will not be as good in the quality department.
+-----+------+-----+-----+-----+I hope this list has been helpful! In the meantime, happy shooting and remember, it's not the gear that makes the photographer.... its the skill/talent. Even horrible cameras can produce amazing results in the hands of an expert. That said though, the glass is the most important part of any photographers arsenal, know what you need and if you are unsure, i HIGHLY recommend renting for a week, to see if the lens fits your needs before you buy. A great place to rent is http://www.lensprotogo.com/! Quality rentals!