ViewfindersPro DSLRs have big, bright pentaprism viewfinders that show 100% of the actual image area. Mid-range models have bright viewfinders, but they don't always give you 100% coverage. Lower-end DSLRs often have pentamirror finders, which are dimmer and show less of the actual image area. Sony's SLT cameras have high-resolution OLED electronic viewfinders rather than SLR optical finders. This, with the SLT fixed semitranslucent mirror design, allows the cameras to provide continuous phase-detection AF at all times, even for video, with eye-level viewing. Some love electronic viewfinders, some don't, especially for action subjects.
Higher-end DSLRs are more likely to offer interchangeable focusing screens and viewfinder angle adapters that make low-angle shooting easier. Of course, with a digital camera, you can always use the external LCD monitor to compose odd-angle shots (assuming your DSLR offers live-view operation, which almost all do today).
Pro DSLRs have big (3.2- or 3.0-inch) state-of-the-art external LCD monitors with 921,000- to 1,229,000-dot resolution, but so do many mid-level and even higher entry-level DSLRs. None of Canon's or Nikon's higher-end cameras has a tilting/swiveling monitor, while some of their entry-level models do. The Olympus E-5 and all of Sony's SLT models have tilting or tilt/swivel monitors. The vari-angle LCD monitors are especially handy for low- and high-angle shooting.