Buying Sony a57 - here is my gear

Have you actually bought this gear yet, or is this the "to buy" list? If you haven't already bought it, I'd suggest considering the Tamron 18-270PZD rather than the 18-200. Depending on what you're shooting, that extra 70mm may come in handy from time-to-time. Given that it's a piezo-drive design you would probably also have a slightly faster and quieter AF on the 18-270 than the 18-200.

Someone else has mentioned it already, but a flash would be handy, particularly if you're gonna do macro. I use the Sony F43 with my A55 and would gladly recommend it (actually, I think this is the one which was recommended by the previous poster). I would also recommend getting a diffuser / deflector to help get the light to subjects which are close to the lens. These can be bought pretty cheaply from most camera stores. For macro shots (I use a Tamron 90) I have a white plastic hood which velcroes onto the top of my flash to help deflect more light directly downwards, and it cost all of $10. Or alternatively you can make your own out of a plastic milk bottle, a wire coat-hanger and some tinfoil. There are lots of DIY examples on the web if you google it.

If you don't want to get an external flash straight away then I would still recommend getting a clip-on diffuser for your in-camera flash - this will improve your close-up flash-lit portraits and flower shots by reducing glare / hot-spots. Something like the Gary Fong Puffer is pretty cheap and works well.

Bare in mind too that camera kits are often built up gradually. So if you don't have the $$s to get everything you need at once, don't despair. Even without the external flash or additional lenses which were recommended such as the 35 F1.8, you've still got more than enough to get you started and ensure many hours of enjoyment. Plus the process of steadily building up your kit as your skills improve (and when you've got the spare cash) is something which I enjoy about the hobby.

Good luck...the A57 is a great choice, so I'm sure you'll enjoy your purchase!