There are several threads around here with all this information, so check some of them out as well.
But here's my 2 cents for getting started:
You have the bike. That's priority.
And a helmet (just remember to wear it, LOL!).
Do you have a method for carrying water with you? Cage and water bottle, camelbak, something like that. That's a big deal to keep hydrated.
For comfort, I'd invest in bike shorts (padded to take the pressure off, and wicking). They don't have to be top of the line, but they will be a *huge* improvement over jeans!
Also pick up a pair of cycling gloves--they'll help your hands immensely.
If you don't want to buy a cycling shirt right off the bat (although the pockets are very convenient), find a wicking shirt. It'll help keep you cool and comfortable.
For personal improvement, pick up a cycle computer. It can be low end to start--something that will tell you distance, speed and time to start. If you want more advanced (and expensive) you can also get one that tells cadence, heartrate, calories burned, all sorts of things.
I bought much of my first things at a cycling store, so I would know what I was getting. The past two years, I've "supplemented" my cycling wardrobe and accessories at a big bike swap (Stop Swap and Save) www.stopswapandsave.com/
Two locations here on the east coast and killer deals, once you know what you want/need.
Although I still love to patronize my LBS (local bike shop)--they give me great service, organize rides, etc--I occassionally buy online. www.nashbar.com www.rei.com www.performancebike.com
That should get you started!
Edited by: DRC2205 at: 5/25/2010 (11:30)