OS X as well as some of the applications come with built-in support for a ton of different (human ;-) languages that you probably don't want to use. You can remove the localization using Monolingual. On my machine Monolingual saved a total of 1.8 GB.
That's about it, really. I wouldn't really recommended removing default applications. One thing some people do is to trim universal binaries down to just the architecture they need, commonly using Xslimmer ($12.95), but keep in mind that's also messing with important things. If you do it, at least don't do it to anything in the System folder.