[G1 Android Development] senab:
I've had a mess with these and removed ALOT of them. Here's the a ls of my /system/app. You can diff against yours to find which ones I've removed (sort the list first though, I used this).

Bear in mind that I've removed stuff which I don't use but you might, so use your discretion. I've removed alot of stuff including Peep (I prefer Twicca), Weather, Various HTC Widgets, Flash, Launcher and various random APKs and it's still working fine.

AccountAndSyncSettings.apk
AccountAndSyncSettings.odex
AccountSyncManager.apk
AccountSyncManager.odex
ApplicationsProvider.apk
ApplicationsProvider.odex
at.abraxas.mountusb.apk
Bluetooth.apk
Bluetooth.odex
Browser.apk
Browser.odex
Calculator.apk
Calculator.odex
Calendar.apk
Calendar.odex
CalendarProvider.apk
CalendarProvider.odex
CertInstaller.apk
CertInstaller.odex
CheckinProvider.apk
CheckinProvider.odex
Clicker.apk
Clicker.odex
ContactsProvider.apk
ContactsProvider.odex
CustomizationSettingsProvider.apk
CustomizationSettingsProvider.odex
CustomizationSetup.apk
CustomizationSetup.odex
DCSImpl.apk
DCSImpl.odex
DCSStock.apk
DCSStock.odex
DCSUtility.apk
DCSUtility.odex
DCSWeather.apk
DCSWeather.odex
DMPortRead.apk
DMPortRead.odex
DownloadProvider.apk
DownloadProvider.odex
DrmProvider.apk
DrmProvider.odex
EnhancedGoogleSearchProvider.apk
EPST.apk
EPST.odex
Facebook.apk
FieldTest.apk
FieldTrial.apk
FieldTrial.odex
FilePicker.apk
FilePicker.odex
Flickr.apk
Flickr.odex
GlobalSearch.apk
GlobalSearch.odex
Gmail.apk
GmailProvider.apk
GoogleApps.apk
GoogleCheckin.apk
GoogleContactsSyncAdapter.apk
GooglePartnerSetup.apk
GoogleSearch.apk
GoogleSearch.odex
GoogleSettingsProvider.apk
GoogleSubscribedFeedsProvider.apk
GSD.apk
GSD.odex
gtalkservice.apk
HTC_IME.apk
HTC_IME.odex
HtcAddProgramWidget.apk
HtcAddProgramWidget.odex
HTCAlbum.apk
HTCAlbum.odex
htccalendarwidgets.apk
htccalendarwidgets.odex
HTCCamera.apk
HTCCamera.odex
HtcClockWidget.apk
HtcClockWidget.odex
HtcContacts.apk
HtcContacts.odex
HtcDialer.apk
HtcDialer.odex
HtcFacebook.apk
HtcFacebook.odex
HtcLocationPicker.apk
HtcLocationPicker.odex
HtcLocationService.apk
HtcLocationService.odex
HtcLockScreen.apk
HtcLockScreen.odex
htcmailwidgets.apk
htcmailwidgets.odex
htcmsgwidgets.apk
htcmsgwidgets.odex
HtcMusic.apk
HtcMusic.odex
HTCNew.apk
HTCNew.odex
HtcPhotoWidget.apk
HtcPhotoWidget.odex
htcsearchwidgets.apk
htcsearchwidgets.odex
HtcSettingsProvider.apk
HtcSettingsProvider.odex
htcsettingwidgets.apk
htcsettingwidgets.odex
HTCSetupWizard.apk
HTCSetupWizard.odex
HTMLViewer.apk
HTMLViewer.odex
ImProvider.apk
ImProvider.odex
jackpal.androidterm.apk
Mail.apk
Mail.odex
MarketUpdater.apk
MediaProvider.apk
MediaProvider.odex
MediaUploader.apk
Mms.apk
Mms.odex
NetworkLocation.apk
PackageInstaller.apk
PackageInstaller.odex
PCSCII.apk
PCSCII.odex
Phone.apk
Phone.odex
PicoTts.apk
PicoTts.odex
restartapp.apk
restartapp.odex
Rosie.apk
Rosie.odex
Settings.apk
Settings.odex
SettingsProvider.apk
SettingsProvider.odex
SetupWizard.apk
SocialNetworkProvider.apk
SocialNetworkProvider.odex
Street.apk
Superuser.apk
Talk.apk
TalkProvider.apk
TelephonyProvider.apk
TelephonyProvider.odex
TtsService.apk
TtsService.odex
UploadProvider.apk
UploadProvider.odex
UserDictionaryProvider.apk
UserDictionaryProvider.odex
Vending.apk
VoiceDialer.apk
VoiceDialer.odex
VoiceSearch.apk
VpnServices.apk
VpnServices.odex
WidgetDownloadManager.apk
WidgetDownloadManager.odex
WorldClock.apk
WorldClock.odex
YouTube.apk