The Panasonic is the shape of things to come, no reflex viewing an' all that, but I don't think the technology is quite there yet. Electronic viewfinder and the autofocusing in particular. Technically it's not a DSLR, but if you've tried one and like it, it will do a fine job.
There are no bad cameras out there now, and it's more what you like the look and feel of for the money. Canon 500D is new and therefore still quite high priced. It doesn't do anything for me that the cheaper 450D doesn't, which it has theoretically replaced, but my choice would be a 40D at that sort of budget. Check out
Camera Price Buster - UKs cheapest camera gear
If you want to get into the full DSLR system thing, then it's either Canon or Nikon. You can get most things for most things, but if it's quality used kit you want then Canon/Nikon have ten times the amount of kit being traded. And there is also nothing better - as good maybe, but not better.