Gmail is my main client. I used to have one with my service provider, but I've moved around a lot lately and figured that something like Gmail would be great. And it is... Tons of storage, a great calendar function that you can share with other useds, it's totally customizable and you can even chat through it to other gmail users. You can easily set your email client with gmail as it is pop friendly and gives you simple instructions on how to do it.
Also, with your gmail account you can set up a fully featured customizable home page which lets you add "google gadgets" with click and drag ease, it's a lot like dashboard. There's a docs and spreadsheets tool that allows you to upload word docs so that you can work on them from where ever you are, no matter what computer you're on. It works seamlessly with blogger, and you can upload images to a picassa web album.
As far as I'm concerned, gmail and it's bits and peices is one of the best tools available for free today. And so far I haven't had a lot of spam, and its filter puts it into a spam folder.
That's all I have to say about that.