600D-body or 550D + 18-135 IS for the same price?

I've been using my little Sony HX100v for nature-video/shots (birding and landscape, mostly) for 1 year, but I'm considering to advance.

I've been looking at 600D and A77 as my short-list options, but I found a deal on a 550D + 18-135 IS for the same price as the best 600D-body. The deal is one-day-only tomorrow, so I'll sleep on this tonight and check answers tomorrow early (Norway-time).

My Canon-plan was to get a 600D + EF 70-200mm f/4L USM, but this will cost me almost the double as this 550D + 18-135 IS deal.

I don't know anything about this Canon 18-135 3,5-5,6 IS. Do you guys think it is going to be useful for any kind of nature-shots or it will be collecting dust in the long run?

Would you guys go for a 600D body-only or 550D + 18-135 IS, for the same price?