Vector formats (for logos):

• EPS (Encapsulated PostScript): The standard if you want to print your logo. These files can be opened in Adobe Illustrator, Freehand or CorelDraw
• AI (Adobe Illustrator): A very popular file format of the most common software (Adobe Illustrator) for vector graphics

Open Formats (for web an print-designs):

• PSD (PhotoShop Document): The standard for website design, Twitter backgrounds and other designs which are destined to be displayed on computer screens. In a PSD, graphic and text is organized in layers so you can easily edit it.
• PDF (Portable Document Format): can be viewed with acrobat reader and will be displayed similar on different computers. But you cannot edit PDF-documents easily.
• INDD (InDesign Document): The standard format for Adobe InDesign.
  With software like InDesign or QuarkExpress, you can create flyers or brochures or other printing material. They are the professional version of MS-Word. Other than a PDF, these files can be edited very easily.

Online formats (for banner): can be opened with any graphic software

• JPG (Joint Photographic Experts Group)
  good compression, small file size but no transparency
• GIF (Graphic Interchange Format)
  Only 256 colours, but can be animated
• PNG (Portable Network Graphic)
  good compression and transparency, but no animations
• SWF (Flash): Can be opened in Adobe Flash-Player or Browser with flash plugin.
  Is perfect for animations and video for websites or banner ads. Interactive content is possible.