Modifier: dexterity
Class skill: scoundrel
While scoundrels are generally ill-equipped to deal with hordes of enemies, the stealth skill gives them a bit of an edge against their foes, by allowing them to sneak past patrols unmolested, hack into computer systems that are behind enemy lines, or plant mines in the midst of a group of enemies. Activating stealth requires a personal camouflage unit, which is provided to a scoundrel at the beginning of the game; more advanced units, which lend a positive modifier to your stealth rank, can be purchased or found later on. Once you activate stealth mode, your character will disappear from sight, allowing you to travel where you wish, provided you don't run across an enemy with keen eyesight. Every time you pass through an enemy's line of sight, that enemy will have the opportunity to make an awareness check; if it succeeds, you can expect to find yourself in the crosshairs within seconds. Your NPC teammates will not join you in stealth mode, nor will they follow you while you're invisible, so if you do find yourself suddenly exposed, they may be too far away to lend you support. If you pump your stealth stat high enough, though, and pair it with state-of-the-art camo gear, you should be as hard to spot as a Dianoga in a trash compactor.
Again, as with some of the other skills here, stealth is a somewhat marginal talent that is not universally useful. Since you're forced to walk while stealth mode is active, using it slows the pace of the game down considerably, but if you're deeply involved in role-playing your character, you may find some interesting solutions to puzzles via this skill.
Modifier: wisdom
Class skill: soldier, scout, scoundrel
Awareness allows all of the classes in the game a chance to spot mines that are in your path or that exist as part of a trap on a door or chest, or expose an enemy that has entered stealth mode. Spotting mines is fairly handy, since you can recover and sell them for extra cash, but seeing stealth characters won't be a consideration for your party, since the only enemies that you encounter that are capable of stealth are apparently immune to awareness. It probably isn't worth your while to pump awareness up too high; it is, after all, a somewhat passive skill that merely seeks to let your character avoid damage. Since your characters cannot die outside of combat, and since there are easy ways to heal your characters, the avoidance of mines shouldn't figure too highly on your list of skill priorities.
Modifier: charisma
Class skill: scoundrel
Having a good blaster at your side won't always get you where you need to go; in fact, since you're unable to indiscriminately cut down the foolish peons who block your way, you may sometimes find that a silver tongue will gain you access to hidden areas and optional quests more reliably than brute force. persuasion is a dialogue-based skill, and isn't useful in every situation, but the ability to win people over with sheer charm will often open up new options and better quest endings for a persuasive character, or allow you to avoid combat with a tentative or gullible opponent. Only scoundrels are able to truly excel in persuasion, but unfortunately, the computer-controlled character creation process seems to discount the usefulness of this skill: if you choose to make a quick character scoundrel, or let the game select the recommended skills in the custom character design process, you will wind up with exactly zero points in persuasion. This isn't necessarily a bad thing, since persuasion isn't immediately useful when you start the game, but you'll want to be sure to pump this skill up at your first level-up to ensure that you'll be able to use it by the time you reach the first planet. Also, keep in mind that only your PC can use persuade; none of the NPC members of your party are apparently gifted with a way with words. This alone makes advancing this skill doubly important for scoundrels.