If one is looking for an insurance cover i have heard that online quotes are usually cheaper than the ones which can be made by agents.So try to get a quote online first from the many companies.

Indeed - a lot of companies generally offer lower fees online because it's all automated - far less need for staff or staff time to be paid for. Plus if you sign up online they may be able to upsell you with further offers to your email address - though you can usually opt out of these in the UK at sign up.

The online rates are cheaper...this seems to be the case in almost anything that you shop for because when you are online, there is global competition (not just local).

Do you have to put more money up front on a policy online? I like the peace of mind of actually knowing the name of an agent I could contact in an emergency. Do you get that with online purchases?

No, it really is generally cheaper - lower costs for processing the applications for the insurers, leading to cheaper sign-ups for customers.

More on that here:
http://www.financemarkets.co.uk/car-insurance.html

I've found that the internet is best for this. Companies also seem to treat their online clients better as well.