In general it's hard to believe anybody could offer something that improves upon Google but sure enough even Google is lacking various features. Whether or not you actually value the features these add-ons offer is something you'll have to find out for yourself. However, most of these services will likely be assimilated or made irrelevant in the future.
Google Reader: AideRSS
This is a rather well integrated way of ranking the bombardment of news that floods your Google Reader. Currently Google Reader has no built-in features for filtering news, so for now this is as close as I've seen anybody get to offering an integrated solution. Another less attractive alternative is available via a GreaseMonkey script, I tried to use it but I think it required more tweaking than I was willing to put up with.
Gmail: Xoopit
I'm not really one for explaining things so you'll probably have to visit the website yourself to understand this. However in my words, it's a way of expanding the Google Mail interface so you can view photos/attachments without digging through your emails.
Google Blogger: Zemanta
Zemanta basically scans what you're typing and offers relevant news articles or links to reference sources like Wikipedia. Another thing that is pretty cool for amateurs like myself is that it helps dig up images that are fair-game or free to use.
