New object parameters
If you have the Object Tools panel visible, pay attention to the lower section of it while adding objects to your scene. Before you transform your new object or go into Edit Mode, you may adjust its initial appearance such as the number of faces.
Animation Playback/Rendering Range
You can quickly set the start and end frames of your animation range by dragging the playhead in the Timeline to the desired spot and hitting "S" for start and "E" for end..
Sometimes your scene gets too complex and perhaps you're using layers and perhaps you are not. But either way, you can select your object(s) and hit NUM / and your selected object(s) will go into a separate area for editing. Just hit NUM / again to return to the normal view.
Use Shift + A to bring up the Add menu. Spacebar no longer works by default in version 2.5.
Use Shift + D to duplicate an object with a unique mesh attached to it (most common duplication method). Use Alt + D to duplicate an object with a shared mesh (also known as an instance). If you've ever used Flash, the instance is like changing your object in the Library and having it update on all objects in your scene.
Use E to extrude a region of faces. But how about a quick way to extrude individual faces? Use the Extrude menu with Alt + E.
Use Shift + B inside the camera view and marquee select a custom area to restrict the render to that box only. This is good to examine just a portion of the render; it can save tremendous amounts of time. You can also check on "Border" in the Render panel to do the same.
Use the View menu and choose Quad View to separate your view into 4 quadrants: Perspective, Top Ortho, Front Ortho and Right Ortho.
Find the small diagonal lines in either the upper-right or lower-left of your view. When you hover your mouse over either of these two areas, a cross-hair cursor appears, indicating you are ready to split a view. Drag either vertical or horizontal to begin splitting, but as you experiment with this, you will see you are committed to the first direction you drag in.
You may also split views the old way of RMB on the view division line and choosing the split option.
Use the same small diagonal lines in either the upper-right or lower-left of your view. If you are joining a view, you must use the corner that is adjacent to the view you want to join and drag back towards it. You will see the same "darkened arrow" from previous versions that indicates which view is going to take over the other one.
You may also join views the old way of RMB on the view division line and choosing the join option.
Drag in Tools/Properties
In a 3D window, if you hover over the small "+" inside a circle at the top-left and top-right of your view, your cursor will become a double-ended arrow. If you use the top-left "+" and pull to the right, you will drag in the Tool Shelf. If you use the top-right "+" and pull to the left, you will drag in the Properties panel. You may also just click on the "+" to make each appear. You can drag them back left or right to hide the panels. Note that these panels change depending on what type of window you are in. See below for hotkey toggles.
Tools Shelf Toggle
In a 3D window, use T to toggle the Tools Shelf.
Properties Panel Toggle
In a 3D window, use N to toggle the Properties panel. Note that this panel holds more properties than the former Transform Properties did.
Use Shift + CTRL + Alt + C to bring up the Set Origin menu. Use this menu to select Geometry to Origin, Origin to Geometry or Origin to 3D Cursor.
Use C to circle select; you no longer have to hit BB.
3D Cursor Reset
Use Shift + C to reset the 3D Cursor at the origin. This is handy if you want to create your next object with its global position at (0,0,0).
Hide/Show Transform Gizmo
If you want to toggle the visibility of the transform gizmo, hit CTRL + Spacebar and choose Enable/Disable.
Align Active Camera to View
Have you ever navigated a view, found a good shot and wished your camera was set up to that shot? Well... you can! Position your 3D view the way you want it and press CTRL + Alt + NUM0. Your active camera will align itself in that direction.
If you want to quickly zoom tight into an area in your scene: use Shift + B, then LMB-drag in your view.
Region to Loop for Texturing
Here's a handy option when you're texturing and marking seams: select faces, whose total boundary around, you want to be the seam, then press CTRL + E and choose Region to Loop. This will select the edges around those faces, making it easier to mark your seams.
Select Linked Areas for UV Texturing
So you've unwrapped your model in the UV editor, and now you want to select all points on a single "island" of UVs. Hover your mouse over one of these islands, and hit "L" to see that all the points in that island will be selected!
Isolate your Model in 3D
This is a fun one to try: hit Alt + B and LMB-drag in your 3D view. Then, rotate around in your view to see that there is a "3D projection" of your isolated model in the view. Hit Alt + B again to return to the normal view.
Quick Toggle for Vertices, Edges and Faces
In Edit Mode, use CTRL + Tab to bring up the Select Mode menu. Then, choose which you want: Vertices, Edges or Faces.
Global - Local Orientations Toggle
To change between Global and Local coordinate systems for your object, hit Alt + Spacebar to bring up the Orientation menu. Your options will then be: Global, Local, Normal & View. You can easily switch back and forth between Global and Local with this method.