This is one of the post I wanted to make for a long time. I thought it would be helpful to beginners. Even people who cook for long time might get some idea about which oil suits which dish most. I hope so :). Anyways since my camera was not available I had to make a post without clicking images hence decided to go with this one!! And being said this readers can understand the pics I used below are only for easy understanding. Have cited the websites for most of them. I have also given which brand I personally prefer :). Hope you find this post interesting and helpful!!
Starting with my most favorite oil!! Extracted from sesame seeds this oil is so flavorful and has cooling effect. This oil works best for all pickles, gravies with strong tamarind base like vendhaya kuzhambu, vatha kuzhambu, kara kuzhambu etc. This oil is not used in general for making dosas or deep fried items. I prefer "Anjali" or "Pasu mark" brand in case I din't get organic ones (Chekku ennai).
I started using this oil very recently after knowing it's health benefits. As the name suggests it is extracted from ground nuts. This oil works best for any south Indian vegetable stir fries, roast, making dosas etc. It gives great flavor to deep fried items like bhajji, pakoda etc. When you use this oil for deep fry remember to add a small pinch of tamarind while the oil gets heated. This will minimize the frothing when you fry the snacks. Any good organic brand works fine for me when it comes to this oil.
As far I have observed this is another under used oil in our daily cooking. But I love to include this oil for any coconut based gravies (kootu), mor kuzhambu, while making adai dosa etc. Even for upma, sevai etc I usually add coconut oil at the end to enhance the flavor of the dish. If the oil is frozen as shown in the pic I find it more flavourful. Currently I use "Keral" brand.
Being Tam Brahm, Ghee is an integral part of our cuisine and I love it :). I use it to temper rasam, sambhar and while making rotis or ghee dosa. While making deep fried sweets adding little ghee makes huge difference. However always melt it to ensure best flavor and minimal usage. I love the home made ghee which my mom gives me whenever I visit home. Other times I mostly settle with "GRB Udhayam" ghee.
Butter is mainly used in north indian cuisine for making parathas, pav bhaji and some rich gravies like PBM. Other than this I use it while making sandwich, cake,cookies and pastas at times. In south indian cooking we use it for making savoury items like thattai, murukku etc. Whenever you use butter ensure it is at room temperature. This will help to spread the butter easily and you won't end up adding more quantity. I generally go for "Milky mist" brand.
This oil is again mainly used in north indian and bengali cuisines for making sabjis and gravies. It has a very strong flavour and this oil has heating effect in our body. Like ground nut oil this can also be used for deep frying pakodas etc. I use "PRO" brand.
After gingelly oil this is my sceond favourite as its so flavorful, tasty and healthy too!!This oil renders great flavour to noodles, fried rice, sandwich, salad, pasta and many other international dishes. Though nowadays people use it for indian cuisine also I personally stick with this oil only when I make Italian, mexican or chinese dishes. Depending on your taste you can select a mild, normal or strong flavored oil. I use "BERTOLLI" brand.
This is an all purpose oil which can be used for any dish while stir frying as well as deep frying, making dosas etc. Since this oil do not have any particular flavour or taste we can use it anywhere. However that is the main reason which make me to minimize using this oil. I use it mostly for deep frying, tempering chutneys and for making cakes. I go for "Gold winner" brand.
Reusing Oil : Usually after deep frying, It is better to let the oil cool down and filter it. This oil can be used to make dosa or any vegetable stir fries.