Ah, lines... now there's a topic that can't possibly be covered completely in a post even as lengthy as one of mine.

Lines are probably the most important component of the whole outfit, all things considered. Some wise old steelheaders have been quoted as saying that lines (not flies) catch fish.

Unfortunately (get used to this theme), there is no silver bullet (at least that I have found) here. I personally tend to prefer double taper lines for their versatility. A weight forward line will cover most steelhead fishing on larger rivers, but a double taper line is superior for roll casting and spey casting in tighter quarters.

If you plan to use the rod primarily for steelhead and salmon, a steelhead taper line is great for long casts and mends.

To further complicate things, some lines work better with certain rods than others. Some rods that are rated as 9-weights will cast an 8-weight line better than a 9, and others will like a 10-weight line better. Again, you will probably want to cast the line first, if possible, but it usually isn't. The good news here is that it will be hard to go too wrong if you have a good talk about lines with your local fly shop bum before buying. You may find you have different preferences, but most of those guys have a solid grasp of what will likely make you happy, and they will rarely steer you completely wrong (unless you ask for fishing reports, of course).

A classic standby that seems to perform consistently with just about any setup is the tried and true Cortland 444. That would probably be a good place to start if you find yourself having a hard time deciding.

Enjoy the shopping, and good luck with whatever you end up with. Whatever it is, buy it soon, because you certainly won't catch any fish without wetting a line; the sooner, the better.