Hi Rajan
As Ankur gave some examinations already which are the top most exams conducted for the entrances into any engineering college.
I would like to add some points to the same it is a normal thing that now a days most of the private colleges have their own entrance level examinations so writing that can help you get seat in that particular college.
If you want to get a chance to enter any college of a particular state then try to write the common entrance for that particular state. Most of the states have their own common entrances for the local colleges. You can find them and apply for those exams.
So writing them can help to get into those colleges.
All the best.

First of all, you must estimate the level of your preparation and only after that you can decide which forms to fill. Although some of the reputed entrance forms are:

1) JEE
2) VITEEE
3)BITSAT
4) SRMJEEE
5) AEEE
and many others...

But its no point spending so much, when you know the result.
Assess your preparation and only after that fill 3-4 forms in the college you wish to target.

Hope it helps!