Various online tools, websites and blogs I use and you should probably too.
- Google Scholar - tool for finding references and citations;
- Morphobank - database of comparative biology, stores various data matrices;
- ResearchGate - also good for finding papers, often has PDFs available as well;
- PhyloPic - good silhouettes of modern and extinct animals for phylogenies and diagrams;
- Paleobiology Database - good for animal taxonomy and paleobiogeography;
- GPlates - good for paleogeography and oceanography;
- Tree analysis using New Technology (TNT) - reliable tool for making and analysing phylogenies;
- The Theropod Database - database of all theropod species and useful information on them;
- Skeletaldrawing.com - various skeletals by Dr. Scott Hartman;
- Google Books - reliable when trying to find old, 19th and early 20th century papers;
- Treatise on Invertebrate Paleontology - you'll inevitably run into this whenever you're researching anything related to invertebrate paleontology;