The Android Marketplace has a collection of mostly free apps. All the good stuff is free, or most of it anyway. Some specialized applications aren't free, and some premium applications. However, I'd say in may case 99% of desired functionality was provided with free apps. Of course, I'm not one for pretty pink themes and such.. and those are the type of things that you'll usually end up paying for. Artists: Take note, you can make money designing cool themes. This is YOUR time to shine, you don't need to be a programmer so long as you have the most basic technical skills.
What I like is the auto-refund policy. I once bought an application, then regretted it once I actually installed the app. As I went to uninstall it, there was an option to Refund my money. I took it. Turns out this is feature, set per application, that allows a set 'trial' period.
Another thing I like is that the market purchases go with your Google account. So, if you have two devices under the same account (e.g. a phone and a Tablet), then only one purchase of an app is needed.
All in all, very well done. The one thing I recommend for ALL Android owners is that they set up and/or configure their Google Account, even if they are a Yahoo or MSN/Hotmail/Live/Bing (hard to keep up with MS virtual presence names) person. Go make sure your privacy settings are like you prefer. Forward your email (just in case). Maybe if you like it, switch to GMail -- it can make the switch painless by importing contacts and mail.
I've always been a fan of GMail, though for most people they seem to prefer 'no change' from whatever they happened to pick that first time they set up a webmail account. If that's you, at least take the time to go set up or configure your Google account. It will greatly assist you in many things, including automatically backing up your contacts and such. Android = Google, so they integrate perfectly. You don't have to change, but you'll get the most bang for your buck (by far) when you go all Google.