One word of warning about the Greabow. Its one negative is that it can't be used mounted. This may not seem like a problem, but one of the most powerful feat combos for an archer is Mounted Combat-> Mounted Archery.. Imp MA etc...
The reason for this is that your mount can get in a full move, while you get in a full attack, at the midpoint of the movement. This lets you rush in to the optimum 30' range and then move out. Forcing most opponents to at least take a half move to get to you, which will if nothing else limit them to a single attack.
Obviously unless you are a race too small to use a greatbow, you can't get your mount in a dungeon and even war horses can be fairly fragile. An exotic mount, can help with this but unless you have a high charisma (unlikely for an archer) all the good ones will require you to be a fairly high level. In the middle levels 7-12, until teleport starts kicking in a major movement option, you will likely be doing a fair bit of overland travel. So it is something worth considering at least.
