There are a TON of distros out there.
You may need to think a bit more about what goals you have, and then decide based upon that.
If you want something that's extremely easy to install, just so you get a taste of how easy linux can be to use, a lot of people love Ubuntu.
I tried it and ran it for a day.
It's got a lot going for it, easy to use, easy to install, tons of packages available, apt resolves dependencies on it's own ...
I personally didn't like it very much, It worked fine, but it didn't suit my tastes.
If you want something a bit more challenging, yet hopefully not overwhelming, Slackware may be more up your alley.
It has a decent number of packages available, the default pkgtool doesn't resolve dependencies, so it does take a bit more work (though there is third party software available to improve things for that.) You set up pretty much everything by editing .conf files, you may encounter occasional hardships. Due to the simplicity of distro, and the general lack of fancy GUI menu's that do everything for you, you're far more likely to actually really dig deep into it and learn a LOT about Linux running Slackware.
If you want to compare distros "head to head" then I'd recommend taking a glance at
http://polishlinux.org/choose/comparison?distro1=Slackware&distro2=Ubuntu
Take them with a grain of salt, but they may help guide you to what you're looking for.
Also, Another site to check out is Distrowatch.
http://distrowatch.com/
From there you can read about all sorts of different distributions, and once you find something that appeals to you, you can go with it.
Personally,
I've got the following distros currently installed:
Slackware 11.0 is running on my server
Slax is running on my laptop (it has a dead hard drive)
Knoppmyth is running on my HTPC (modified version of Knoppix with mythtv built in)
I've played around a bit with Other distros in the past including older slackware distros, several old redhat distros, and a couple of old Mandrake distros. I also tried out FreeBSD 4 several years ago, but I really didn't know what I was doing at the time.
Currently, I've got VMware server installed on my main Windows PC and I'm toying with OpenBSD 4.0. I'm planning to install Arch Linux next (I've downloaded the ISO, but I haven't had time to install it or play with it at all yet.)
In conclusion, any distro should work decently, you will learn more with some than others. Choose what you think fits you the best. If this decision is too overwhelming due to the number of options available, then I'm gonna toss up the name Slackware again, just because it's my personal favorite.