Special for BlackBerry Secrets Codes

Hold “Alt” and press “N”, “M”, “L”, “L” (repeat to reverse the effect).
In the Address Book, hold “Alt” and press “V”, “A”, “L”, “D”.

Forces a data structure re-build in the Address Book…
In the Address Book, hold “Alt” and press “R”, “B”, “L”, “D”.

Displays the source code of a Web page.
In the Browser, hold “Alt” and press “R”, “B”, “V”, “S”.

Provides crucial technical information about your device, for when seeking technical support or help in forums…
Hold “Alt” and (left) “shift”, then press “H”.

Displays your device’s international mobile equipment identity (IMEI – your serial number) on-screen… Also works from all other GSM handsets.
Type “*”, “#”, “0″, “6″, “#” on the Home screen.

Performs a “soft” reset of your device; the equivalent of doing a “battery pull” (ie. Removing the battery for a few seconds).
Press-and-hold “Alt”, then press-and-hold (left) “shift”, then press-and-hold “Del”.

Displays event logs of all the system-level events that occur on your device…
Hold “Alt” and press “L”, “G”, “L”, “G”.

All of these secrets have been tested on the BlackBerry 8800 and BlackBerry Curve 8300 .

In some cases, you will need to be on the Home screen when you enter these codes…

A or C = phonebook
S = search
F = phone profiles
W or B = browser
H = help
K = locks the keys
L = calendar
V = messages
M = messages folder
R = alarm
T = tasks
U = calculator
I = applications
O = options
P = phone

Some new additions thanks to the contributions in this thread:

T – Top of page (in browser)
B – Bottom of page (in browser)
Space – Page down (in browser)
ALT + Right Shift + Del = hard reset
D – Memo pad
U – Switch between hide/unhide in title bar (in browser)
ALT + NMLL = numbers instead of bars for signal strength