Rapid hyperspace travel
Asgard hyperdrives have routinely proven capable of crossing intergalactic distances in a matter of days, even hours, and are a necessity for the Tau'ri to continue their intergalactic endeavors.
The precise speed of a vessel equipped with an Asgard hyperdrive appears to be directly proportionate to the ship's available power. The Prometheus needed months to travel between the Milky Way and Pegasus galaxies. However, the more advanced Daedalus routinely made the trip in about 18 days. The drive could be modified to allow the ship to travel faster, but it would risk burning out the drive. An Asgard vessel, or a Daedalus-class ship with a ZPM tied into its power systems, could make the trip in about four days. The Asgard O'Neill-class vessels were capable of travelling from the Ida galaxy to the Milky Way in only a few hours. Even without a ZPM or comparable power source backing them, these are some of the fastest hyperdrives known to exist, surpassed only by a fully-powered stardrive. (SG1: "Prometheus", "Prometheus Unbound", ATL: "The Siege, Part 2", "Critical Mass", "Misbegotten")
While in hyperspace the shields and weapons systems of a ship using an Asgard hyperdrive are offline, due to the fact that the full power of the vessel's generators is required. As a result, a ship using an Asgard hyperdrive can be destroyed if a nearby vessel in hyperspace self-destructs; however this occurrence is highly unlikely, as no other hyperdrive has been seen keeping equal pace with them. Asgard ships have the ability to tow other vessels in their hyperspace field, but this causes the total travel time of the journey to be lengthened exponentially (it is unknown if the hyperdrives equipped on Tau'ri vessels have the same capability). (SG1: "Unnatural Selection", "New Order, Part 1")
An Asgard scoutship that had been in mothballs for thousands of years proved to be fast enough to travel between the Pegasus Galaxy and Earth in around fifty hours. Also, to the Atlantis team's surprise, the hyperspace transition is so smooth and seamless that it is unnoticeable until its pointed out that they have made the jump to hyperspace. (ATL: "Stargate Atlantis: The Third Path")