Hello there

I have several projects on the web with many customers, what would be the best CRM system for me in your opinion? many web sites many services...

I need it to be PHP based.

I want it to be for support requests only - and I want it to replace the email - what do you recommend?

Cerberus Helpdesk would probably work perfect for you.

I would suggest you look at http://www.kayako.com it's a very well rounded product and can pipe emails direct into it's ticket system and is php based.

Are you looking for a helpdesk or a CRM?

Both, I'm trying to reduce the amount of support requests sent to my email address.

OK.

If you want a helpdesk then Kayako would be the solution, but it is not a CRM.
For CRMs you could look at Sugar CRM