There are many different types of arches. Packed arches consist of multiple balloon clusters strung together to make patterns. Spiral patterns like the ones above are probably the most well known.
Pearl arches are single balloons attached directly to monofilament line. Often they have tulle or ribbon suspended from each balloon.
There are also arches made of linking balloons, eliminating the need for monofilament line or framing materials.
Arches that need to last for several days or weeks can be filled with nitrogen or air and constructed on a frame. This would include shapes such as hearts or stars.
Some examples of other arches can be found on the "Other Arches" page.