I want to buy an external flash light for my Canon EOS 400D. Is HF-DC1 good enough or is it designed for more compact cameras?
Any suggestion on alternatives?
Canon HF-DC1 is designed for Canon PowerShot product line only and incompatible with DSLRs. You can get Canon 270EX which is about the same price range. Other relatively expensive options will be Canon 430EX II and Canon 580EX II.
Also there are 3rd party (non Canon branded) flashes, which are cheap. But most of them do not have automatic (TTL) mode and all settings have to be done manually.
It depends on what you want to light. It is very hard to get interesting photos with the strobe/speedlite on the camera -- you have to move the light off camera so that the light comes in at an angle.
There are literally hundreds of books/dvds/courses on off-camera lighting. One great free resources is the Strobist site: http://strobist.blogspot.com/
Do not be afraid of manual strobes. The Strobist is a big fan of inexpensive manual strobes. A flash like the LumoPro LP160 is inexpensive, but not cheaply built. It is very flexible and a great tool.