$500 is a great budget to start actually.
I started playing with off camera flash photography about a year ago and have built up a nice little setup that I think would match your budget.
First off, you want some speedlites. I also have a 7D and yes, you can use Canon brand speedlites to trigger wirelessly. The problem is, if you are outside in bright sunlight or there is not a direct line of sight between the camera's flash and the speedlite, it wont trigger. A solution to this is to get wireless triggers. Pocket wizards are the best, but they are very expensive and will probably take up all of your budget. I would suggest to get something cheap to start like some Cactus triggers (I have cactus V2s that I picked up from ebay for 35 shipped. Came with 1 transmitter and 2 receivers).
The canon brand speedlites are also a bit expensive (250+ to start for a 430EX II for example). I have one 430EX II but recently picked up two Vivitar DF383 flashes. They work amazing and have had no problems and cost me about $125 each on amazon shipped.
You'll need some light stands now. You can get light stands for about $20 or $30+. I personally picked up two manfrotto nano light stands at about $50 a piece. They are great because they fold up quite nicely and are great for traveling but unfold to a very nice size lightstand which you can use for all of your work with no problem.
Next you'll want 1 or 2 shoot through umbrellas. You can get these for about $20-$30 each as well. Brand doesn't really matter here.
Lastly, you need an adapter for your lightstand to hold both the flashes as well as the umbrellas. You can get these for about $30 each.
If you add all that up (assuming you get two of each):
(2) Vivitar DF383 @ $125 each
(1) set of Cactus V2s recievers/transmitter @ ~$35
(2) manfrotto light stands @ $50 each
(2) shoot through umbrellas @ 25 each
(2) umbrella/flash adapters @ $30 each
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Grand total of approximately: $495.
I think that's a great start and pretty much resembles exactly what I have currently.
Please note though that I do not use ETTL. I'm all manual when it comes to the flash power/zoom as well as manual mode on my camera so I use the aperture/shutter speed to control the type of shots I produce. If you want to shoot ETTL with a wireless system, I think pocketwizard just came out w/ something that allows you to shoot wirelessly with their system without losing ETTL functionality. It's a bit pricey though (but worth it if you want to still use ETTL). Personally, now that I learned how to control the light manually, I have not used ETTL.
Check out this blog post I did a few days ago with a picture of the gear if you want a better look. Hope this helped!
http://www.jasonsanchezphotography.com …r-portable-lighting-setup