Some of my favorite applications are iGoogle Homepage, Google Reader, Gmail, Calendar, Blogger, and I use each of them multiple times a day.
And it is expanding: Google now owns YouTube, Feedburner, and Picasa (pictures), and I also use it exclusively for maps and document sharing. Really, it just goes on and on and on.
The only Google application that I don't like is Google Groups, as I personally think it is extremely outdated as far as forum options go. Its only redeeming factor is that I can use my Gmail address to log in. And I am ambivalent towards Google Wave currently, I have an account but so far it seems to do exactly everything I can already to with Gmail, but only with people who also have Google Wave. But two apps out of the many that I use regularly are completely okay with me.
And here is what makes me love Google, instead of simply appreciating their services. They are funny. They are cool. They, as a company, have a personality and a sense of humor. Google is well-known for the always current logo changes, easter-eggs, and April Fool's jokes. And all of it pales in comparison to their Artist Themes.
Themes are used to decorate your webpage. Google has an entire category for artists, and I am really impressed with their selection. There is a wide range of styles, from Modern to Grunge to Pop to Scrapbook, and a variety of media, like photography, paint and digital. It is web browsing eye candy covered in awesome sauce.
iGoogle Homepage Artist themes
Each theme usually has 3 or more images, so you get some variety every time you load your page.
There are so many, I can't even list all the ones I love. In addition to fantastic art, they also have themes from some of the biggest names in Music (Bob Dylan, Beastie Boys, Coldplay), Fashion (Prada, Gucci, Kate Spade), Games (WoW, Zelda), Decorating (Martha Stewart)... pretty much any interest you have, you can decorate your page with it.
I even have a different theme for every tab in my iGoogle, which both helps me remember what page I'm even on, and gives me something new to look at in each place. There is so much variety offered in the themes that I change them often. I love it, love it, love it.
(P.S. If you are wondering, I don't get anything for posting this- I just like to share cool stuff that I enjoy with others.)