On the Floor
I've been finding most of these shortcuts by accident. Usually by missing a usual shortcut with an inaccurate keystroke, then sudden, unexplained magic happens.
I've also discovered quite a few while watching Railscasts. If you watch the upper right hand corner of a Textmate shot you'll usually see what sort of shortcut is used to make the magic happen.
Here's a few I use all the time:
Cmd + T : List of most recent files and quick file search
Ctrl + Shift + D : Duplicates you current line/selection
Ctrl + Shift + K : Removes the entire line the cursor is on
Ctrl + Cmd + R : Show the file you are working on in the drawer
Alt + Cmd + Down : Opens the view of the action your cursor is currently in
Ctrl + L : Inserts " => " (in an .rb file)
Cmd + ] or Cmd + [ : Indent left or right
Alt + Cmd + ] : Align assignments within a block
Cmd + / : Comments out the line/selection of code using the appropriate syntax (most of the time)
Cmd + Del : Deletes everything after the cursor
Cmd + Backspace : Deletes everything before the cursor
This, like terminal, works more often than not. Depending on the bundles you have installed and the extension of the file you are coding, hitting tab following some snippet of code may complete what you are doing. You can also continue to tab through the options in blocks that have more than one condition/option/variable.
Def then Tab : def method ... end
Do then Tab : do |variable| ... end
If then Tab : if condition ... end
vp then Tab : validates_presence_of :attribute, :on => :create, :message => "can't be blank"
vu then Tab : validates_uniqueness_of :attribute, :on => :create, :message => "must be unique"
vf then Tab : validates_format_of :attribute, :with => /^[\w\d]+$/, :on => :create, :message => "is invalid"
bt then Tab : belongs_to :object, :class_name => "Object", :foreign_key => "object_id"
hm then Tab : has_many :objects, :class_name => "object", :foreign_key => "reference_id"
ho then Tab : has_one :object, :class_name => "Object", :foreign_key => "object_id"
mcol then Tab : Provides you with the options available for column migrations
mtab then Tab : Provides you with the options available for table migrations
Ctrl + Cmd + T : To see a list of all bundle items (shortcuts) available to the file you are currently working on
You can also make your own by recording and saving a Macro. In the menu under Bundles > Macros you can:
Ctrl + CMd + M : Start recording. This will record any keystrokes you make so that you can create your own shortcuts.
Shift + Cmd + M : Replay the last recording to see how it works or just repeat the last recorded action over and over.
Alt + Cmd + M : Record the last recording and assign a shortcut to it.
There are tons of bundles and shortcuts you can add use in textmate and this is only scratching the surface. Give it a shot and see what you find.