Melee fighters can be very dangerous when fighting opponents that focused on ranged combats. This is especially true in tight places (space stations & ships, cities), when there is little room for maneuvers.
These melee fighters fare well when using Trips (especially Improved Trip - see Monks) or Grapples. Pressing Attack is a "must" Feat for these guys.
Disarms or sunders might be useful as well.
This can be compensated when the ranged-fighters have the tumble skill (and do not steadily suffer from AOOs - remember an AOO may not be a regular attack but also a trip!)
Mechanist can pose a serious threat in melee when attacking opponents using ranged weapons or Power Armors (sabotage)
Remember this if some of the players want to play Monks or maybe Barbarians.
Speaking of Barbarians:
If someone wants to play one, be aware that Rage is useless in Ranged combat (except you maybe able to carry a heavier weapon, which is rarely a problem), so remind him of this.
(Or "invent" a new Feat that grants some benefits - I used "Rambo`s Rage", which effectively increased the size of the character when figuring out what ranged weapons he might use.
I also adapted the Monkey Grip Feat for this, and allowed the user to ignore the penalties for using long-arms onehanded.

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Another, interesting character class: Rogue.
For NPCs as well as PCs - using Ambidexterity and Two Gun Shooting, he might use a Taser in his first hand and a Blaster Pistol (or silenced Autopistol) in his offhand. Taser stuns opponent, opponent loses Dex Bonus, opponent suffers from sneak attack.
(Though you might rule-zero this - I did not, but until now, no one could use it)
Speaking of Rogue, I must think of Skill Points:
There are some useful and probably neccessary new Skills - many players might find their characters have to few skill points.
There are some ways to deal this:
a) Tell them to stop whining.
b) Consider using a highter point-buy (if you use point-buy), so they are able to get a higher Intelligence
c) Bump up skill points per level (approx. +2 / level)
d) Remove some not really useful skills or skills that seem to overlap:
Cryptography and Decipher Script could be defined as one skill
Appraise might be a Knowledge Skill (does not really change something) or becomes part of the Diplomacy Skill.
Maybe combine skills like Balance, Tumble, Jump, Climb. (maybe Acrobatics - Balance & Tumble; and Atlehtics - Jump and Climb. Not sure if this makes sense

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Urban Lore could be instantly dropped and combined with Gather Information.
Handle Animal and Animal Empathy might become one skill (and make it a special abilities from Rangers and Druids to use it in an Animal Empathy way?)
Mustrum Ridcully