Use keyboard shortcuts to switch between applications in android:

Don’t forget to bookmark this page, this is a long one!

If you want to create your own shortcuts: Settings > Application settings > Quick launch

Open applications:
Browser SEARCH + b
Contacts SEARCH + c
E-Mail SEARCH + e
Google Mail SEARCH + g
Calendar SEARCH + l
Maps SEARCH + m
Music SEARCH + p
Messaging SEARCH + s
YouTube SEARCH + y
You can add/change these here: Settings > Application settings > Quick launch

Scrolling tips:
Page down SPACEBAR
Page up SHIFT + SPACEBAR
Jump to end of list ALT + TRACKBALL roll DOWN
Jump to top of list ALT + TRACKBALL roll UP

Typing and text navigation tips:
Insert special character ALT + SPACEBAR opens special character selector
Delete character to left DEL
Delete character to right SHIFT + DEL
Delete entire line ALT + DEL
Persistent CAPS Press SHIFT twice; press SHIFT again to escape
Jump cursor to beginning/end of line ALT + roll TRACKBALL left/right
Create tab character ALT + q
Highlight (select) text SHIFT + roll TRACKBALL
Cut text MENU + x, or Highlight text, press & hold TRACKBALL, select Cut
Copy text to clipboard MENU + c, or Highlight text, press & hold
TRACKBALL, select Copy
Paste text copied to clipboard MENU + v, or Highlight text, press & hold
TRACKBALL, select Paste
Undo change MENU + z
Select all text in field MENU + a, or Highlight text, press & hold
TRACKBALL, select Select all

Browser tips:
Open Go to window MENU + s
Open Bookmarks MENU + b
Open Windows MENU + w
View history MENU + h
Refresh or stop page MENU + r
Go back a page MENU + j
Go forward a page MENU + k
Find on page MENU + f
Go to home page MENU + ENTER
Zoom in MENU + i
Zoom out MENU + o
Go to Settings MENU + p
Page down SPACEBAR
Page up SHIFT + SPACEBAR

Map shortcuts
Directions MENU + d
Select map mode MENU + m
History MENU + h
My Location MENU + 0 (zero)
Go to Settings MENU + p
Zoom in MENU + i
Zoom out MENU + o

GMail shortcuts (while viewing message)
Forward F
Reply R
Reply All A
Archive Y (works on list mode too)

Other Google apps:
If you are in the mood for more shortcuts on any google apps like mail, calendar, docs, try typing: “?” in the webbrowser when using that app.
You would need to enable this option in settings for mail. The other apps have this enabled by default.

source : http://android-tips.com/