The xbins website is great for listing what each program does.
I've been thru a lot of them, and had heaps of crap on my xbox. I never used most of them so have now removed them. I basically have kept only what I need, and only the one app in each "section" that I like the best...
so....
I use Ava for my dash (and have Evox on there also acutally, linked to from Ava, but I never use evox anymore).
dvd2xbox for file copies
xbmp and xbmc (I use xbmp mostly, and check out the regular xbmc builds out of interest) for media playing
config magic for hdd/eeprom settings
enigmah video switcher to switch between NTSC and PAL modes
And that's about it really...ava has a built in FTP client AND server (good for xbox -> xbox copies, meaning no need to a seperate FTP client app), and a built in file manager (no need for boxplorer or xcommander, and I use my pc via ftp for the rest)....
So really, that's about half a dozen apps.... your personal choices may yield different results. I also have a lot more PC apps I use to do xbox things, like dvd burning, ms dash hacking etc....