Here is a small list of shortcuts that I frequently use on my Pearl. I will keep updating as and when I find more shortcuts – if you know some shortcuts, post as reply to add to this list.
Introduction to keys:
The ALT key is the first bottom key on the left side of your keyboard; looks like
for T-Mobile and
for Cingular Blackberry Pearl phones respectively. The CAPS key is the one located second bottom key from the right side of your keypad; looks like
for T-Mobile and
for Cingular Blackberry Pearl phones. The ESC key is the one located immediately left to the trackball on the top of your keyboard and looks like 
When I mention ALT+KEYS means while pressing and holding ALT key, you have to enter the sequence K, E, Y, S on your Blackberry keyboard.
HomeScreen Shortcuts:
ALT + LGLG = Event Log is displayed. From menu options you can select ‘Clear Log’ to clear the log entries – though this does not have any significant improvement in performance; it is better to have it free if there is no problems.

ALT + ESC – while on any application to switch between applications. This saves time from exiting current application and running other application and allows multitasking of applications in your Pearl

ALT + NMLL = change signal display to number or bars. (Note: to enter N – you have to enter the key BN twice – something similar that you would do on multi-tap)

ALT+RACE/Select Options->Advanced Options-> Applications, ALT+CAPS+H = launches Help Me! Screen with information about your device at one place.

While at Homescreen – enter a phone number – allow you to call that number.

Applications Screen Shortcuts:
A – Address Book
R – Alarm Clock
B – Browser
U – Calculator
L – Calendar
C – Compose E-mail
K – Keyboard Lock
M – Messages
D – Notes
O – Options
P – Phone
F – Profiles
V – Saved Messages
S – Search
T – Tasks
W – WAP Bookmarks
Smart System Codes while on an Auto-Text input field:
Type the below smart system codes and press ENTER to get these text replacements.
Myver – Displays the device/version
LD – Displays the local date
LT – Displays the local time
mysig – Displays the information you entered in the BlackBerry Options -> Owner screen
mypin – Displays your handheld’s PIN

Messages application shortcuts:
ALT+V/ALT+C = Voicemail messages

ALT+P/ALT+O = Placed call logs

ALT+I/ALT+U – Incoming call logs

ALT+A/ ALT+S – SMS messages

ALT+L – Compose a new e-mail message