According to Eurogamer, the Guild Wars expansion, Eye of the North, is due out at the end of August 2007:

NCsoft has revealed that Guild Wars: Eye of the North will be available on 31st August for GBP 24.99.

It's touted as the first expansion in the series, despite being the third paid-for update. Factions and Nightfall were campaigns, you see, so Eye of the North is the start of a new direction for developer ArenaNet. GET IT RIGHT.

It's all about rewarding the existing fan-base, apparently. The veterans. So, rather than introduce lengthy campaigns designed to ease new players into the fray, ArenaNet can focus on expanding the elements that have kept old-timers loitering around.

So, that means you'll be treated to 18 meaty new dungeons, 150 new skills across all professions, 40 new armour sets, 10 new Heroes, new weapons, new items and titles. Eye of the North will also act as a bridge to Guild Wars 2, allowing you to carry titles and accomplishments over using The Hall of Monuments.