Mascaras have been around since 4000 B.C. and hence are one of the oldest cosmetics known to mankind. Long lashes are a universal sign of beauty and femininity. From an evolution point of view, I'm guessing it is tied to attractiveness: long fluttery lashes --> flirty --> mating and procreating; and that's all evolution is about, maximizing your chances of mating and procreating ( leaving procreation aside, not much has changed ;) )
Here are 3 products that I have personally used and can vouch for from my personal experience.
1) L'oreal Lash Serum: 3rd one in the picture below, available for $12 to $15 in the US. It is a plain and simple conditioner for your lashes. Pop it on each night before you sleep and I guarantee you will see a difference in 3-4 weeks with daily application. I have noticed however that the difference is fairly small and goes away as soon as you discontinue the application. All in all, this is a great no hassle product and I highly recommend it.
2) Smartlash Eyelash Enhancer (does not contain prostaglandin): 2nd one in the picture below, available for $25 to $35 in the US. It is a bit better in terms of lashes. It has a thin brush for applying it to the base of lashes but apply too much and you get it in your eyes and it burns! So be careful. Avoid the product if you have sensitive eyes. I definitely see results from applying this one in 3 weeks or so as well. However, after a while, the results plateau. It is still not as extreme in terms of results like Latisse (contains prostaglandin) or some higher grade products. All in all a great product, if you know the risks associated and don't want to spend a bucket load on eyelash treatment.
3) Mix of Castor oil and Avocado oil (placed in a l'oreal lash serum vial for ease of application): The most natural one on the list and is the 1st from left in the picture below. Castor oil is a very popular
I have always had average lashes but with the use of the above mentioned products, they're getting better. Below, 1st pic shows my bare lashes with only the oil applied to them, 2nd pic shows my lashes with one coat of the L'oreal Butterfly Lashes Mascara (sorry for the freaky looking, poor quality pic).
I bet if I was more regular with the application of these products, I would see a bigger improvement.