There are websites that do an interesting comparison on interest rates for various tenures. Interestingly, they not only do PSU bank interest comparison, but, also compare private sector banks, institutions, post offices and company deposits.
For example, these websites could tell you that at the moment Shriram Transport Finance FD's offer you the best interest rate amongst all institutions for a five-year deposit.
Interestingly, these websites can offer you interest rates for varying tenures and across different category of institutions. For example, if you prefer a post office and company deposit, they can do a comparison of both simultaneously.
On the other hand they can do a comparison of PSU banks, private banks and other institutions like HDFC and public companies like Tamil Nadu Power and Kerala Road as well.
It's best to visit these websites, so you do not miss on the higher interest rates. However, keep in mind the highest interest rates, need not always be the safest.
When investing in a company fixed deposit remember that it carries a risk, in comparison to a public sector bank fixed deposits. On the other hand company's FDs can charge a higher rate for breaking your fixed deposit and may not be as liquid as bank FDs.
To read more on the merits and demerits of a company fixed deposit read /classroom/2012/04/company-fixed-deposits-investments-its-merits-demerits.html
Also, if you are likely to invest now, it's best that you lock your money in fixed deposits for a longer duration. This is because there is every possibility that interest rates may fall and you would have locked your deposits for a longer duration at higher rates.