I have a reseller account, and one of my client need SSL. To have SSL, I need dedicated IP address. Do I have to take dedicated IP address for the client only? or
since it is under my reseller account, and if i take dedicated IP, my clients can use? If that is the case, if couple of my clients want SSL, how is it going to work?

Each separate domain that needs SSL will need a separate IP address. Each IP will be tied with a domain.

Indeed, unless you are going to setup a shared SSL, you'll need one dedicated IP per SSL Certificate.

Good to know. Thanks guys.

I am planning to use https as a default communication protocol on my reseller site (forced encryption, heavier on the CPU but who cares), so I guess atleast few dedicated IP's are mandatory for me.

You need a dedicated ip to install ssl per domain.
You can use dedicated ip on reseller domain and use it as shared ip for all hosting accounts under your reseller account instead of server shared ip.
That will give you a little more anonymity.

You can resell IP for your customers as well. Just do not get bunch of IPs to reserve, because you will pay for them monthly and you might not resell all of them at once. Why pay for unusable IPs ? ;)