With the lens of the 400D kit, you can either:
Get a modern version of the 18-55. But it's a bit of a minefield, because Canon has reintroduced a version without an operating system for low-end cameras. So make sure you have IS, IS II or IS ISTM (on a 400D, the STM is not very useful as a "video" lens, but you can take advantage of the non-rotating front lens). Since these are kit lenses, many are available on the market of the occasion if you want prices unbeatable.
get something a little more expensive but a bit faster and more extensive, like the Sigma 17-70 f / 2.8-4 (the SI or the IS contemporary)
- or something faster with less reach: a 17-50 f / 2.8 of different brands (Sigma, Tamron)