Syryous:
If dragon magazine material is allowed, Dragon Compendium have:
DEAD EYE [GENERAL]
Your precision with ranged weapons translates into more telling strikes than you could normally make.
Prerequisites: Dex 17, Point Blank Shot, Weapon Focus (any ranged weapon), base attack bonus +14.
Benefit: You may add your Dexterity bonus on damage rolls made with ranged weapons for which
you have the Weapon Focus feat, so long as the target is within 30 feet.
Special: Dead Eye does not increase the damage dealt to creatures immune to critical hits.
A fighter may select Dead Eye as one of his fighter bonus feats.
Author: Clifford Horrowitz. Source: #304.
Note that the errata lowers the BAB requirement from 14 to 1.
I have some other hints, neatly lined up in this topic:
http://www.brilliantgameologists.com/boards/index.php?topic=9073.0It's a bit of a bundle of hints, so I'll list the good stuff:
Hit and Run-Fighter.
Targeteer from dragon magazine 310. Wait a sec... *looks at the STR score*... no, let's ignore Targeteer.
Craven.
If you can stomach the -7 ability points you get from a +1 level adjustment template, there's pretty much nothing better than the Dark Template from Tome of Magic. Relevant stuff that it gives are:
Hide in Plain Sight, Hide +8, Move Silently +6, Darkvision 60 feet, superior low-light vision.
You also get resistance to cold 10 and +10 feet to all your movement modes (you got a swim speed, that's neat), good if you have to run away from a cryohydra or something.
Picking up Item Familiar (a feat) from Unearthed Arcana (let's you invest skill points into a magic item you have to make it better) allows you a bonus to a skill. For every 3 skill points you add to it, you get a +1 bonus.
Combine this with Open Minded from the Expanded Psionic Handbook that gives you 5 skill points, you can eventually have an item, let's say your cloak of elvenkind or your +2 dex gloves, that gives you a +9 bonus to Hide.
It's one heck of a Feat investment though, so by that point you might have been better of picking up other Feats.
Oh and I don't know if Muckdwellers gain automatic poison use, if they don't then I'd recommend you to substitute your Trapfinding for Poison use.
It's an ACF in DotU for rogues.
Speaking of poisons, there's a feat from DotU that nets you +2 DC to the poison save for -1 SA die. Could be an idea.