apps i deleted from system:
hookt.apk (boost mobile app)
aurora.apk [.odex file too] (didnt like this live wallpaper)
bluesea.apk [.odex] (same as above)
bluetooth testmode.apk [.odex] (im not sure if you need it tp make pairings but i havent so far so i think its safe)
booksphone.apk
deviceselfservice4005boost.apk
factorytest.apk[.odex]
forest.apk[.odex] (another wallpaper i didnt like)
geniewidget.apk (great weather app to keep but it is deletable)
googlequicksearchbox.apk
keyboardslideupcounter.apk[.odex] (counts how many times you use the physical keyboard that prevail doesnt even have)
keytracer.apk[.odex](sounds like it can read your messages so i took it off no probles happend without it)
laylar.apk
lcdtest.apk[.odex] (cant test it anyways)
livewallpapers.apk[.odex] (only if you dont like the moving wallapapers, they do drain battery a lot faster and slow the phone down a bit)
poynt.apk
scvngr.apk
spark.apk[.odex] (livewallpaper)
sprint_installer.apk (no problems when i deleted it)
sprint androidextension.apk ( no problems either, deleted with sprint installer at the same time)
swype.apk (too much ram used, and a chunk of internal memory regular keyboard is fine. or vise versa)
talk.apk
talkback.apk
thinkfree.apk
visualisationwallpapers.apk[.odex] ( for if you dont use them they are deletable)
voicedialer.apk[.odex]
voicesearch.apk[odex]
apnservices.apk[.odex]
zone.apk
Extras:
launcher2.apk[.odex] (you can use a better launcher or even a faster one that uses less memory just make sure to install a launcher before deleting this one)
Gallery3Dapk[.odex] (quickpic is a good alternative if you know how to install it as a system app, it also works as a user app)
hiddenmenu.apk (if you dont plan to tweak your phone any longer or not at all. itll just be there) have not tested how it works without deleting.
phonesky.apk (aka market aka playstore. update first. delete old one. transfer .lib files where they need to go then move apk.. less memory wasted, and more ram)
picotts.apk[.odex](if you dont use txt to speech or GPS maps or "talking apps")
soundrecording.apk[.odex] (dont have problems when i delete it, make a backup on the sdcard first "copy n paste" both odex and apk files just in case)