[Mad Hamish]

There's Reakt, suprathyroid, reflex boosters and initiative modifiers (wired reflexes, move by wire etc)
but what other augments are there that can be used to boost your defense rolls?

I've seen people suggest that it's easier to boost Gymnastics for dodging rather than dodge but I'm not sure what's available to do so

[Critias]

There's also the genetic (short-term) treatment Sideways.

For Athletics boosts, there's always the good ol' Synthacardium bioware (from the core book).

[TheNarrator]

Also useful for boosting Gymnastics (for the purpose of gymnastic dodge) is Enhanced Articulation, which improves all Physical Skills linked to physical attributes (which is all Athletics skills, half the Stealth skills, an a few others).

The best boost to defense, however, is probably Combat Sense, which is only available as an Adept Power or a spell. Street sams tend to be better at resisting the damage than dodging the bullet.

[Lichtbringer]

i think a tacnet can give you bonus dice on combat related rolls, including dodging.

[FuelDrop]

An absolutely obscene amount of firepower. After all, the best defense is an overwhelming offence, right? 

More seriously: stick and shock, smoke grenades, flash-packs... anything that penalizes the person shooting at you may as well be bonuses to your defense. also, a holo-projector putting out decoys can draw fire from any hired muscle that fails their perception test, at least for one initiative pass. An auto-miss is better than any number of extra dodge dice, as it doesn't even reduce your pool for dodging anyone who didn't fall for it.

[Makki]

cover adds dice to dodge. so does running

[esprism]

I play a high dodge character but honnestly it's quite useless.

11 Reaction (max 12) (surge + genetic + move by wire)
9 dodge (6 natural + 2 move by wire + 1 reflex recorder)

and Synch give one additional dice after ennemy 1st attack for all combat tests including dodge

5 natural rea + mbw give 9 rea
4 natural dodge + 2 mbw give 6 dodge

It's better to keep 6 rating skill for attack or something more effective

[Mirikon]

I believe there's bioware called a skill recorder that allows you to add +1 to a skill or skill group. Put it in Dodge (or Gymnastics, if that's your thing).

After that, you can play with visibility bonuses. Smoke, invisibility spells, and the like all work to make you harder to hit.

[TheNarrator]

Reuthenium-coated armor and a suppressed weapon. They can't shoot back if they can't tell where the shots are coming from. 

Also, the value of taking cover in a firefight cannot be overstated.

[Critias]

I play a high dodge character but honnestly it's quite useless.

I have to disagree there.  I've run characters that aren't nearly that min/maxed towards having high defense pools, and it's helped out plenty.  Sure, if the GM does nothing but spam spells and explosives at you you're still hosed, but basic math tells you that it's better to have a great defensive pool than not.  A guy as powergamed as yours, slinging about 20 dice to avoid incoming attacks?  I'm not sure how that's "useless," when you compare it to the average incoming NPC attack pool.

[esprism]

My opinion is that correct dodge is mandatory but max it out is too expensive compared to good damage resistance.

i have 23 full def for bullets and 30 for melee full def and 6 edge but even with that sometime i take high damages.

Of course most of the time i don't suffer much but it's more efficient imo to have a correct 15 full def dodge for bullets and good damage resistance.

[UmaroVI]

It's not that full defense is useless, it's that people tend to seriously overvalue it and focus too much on it at the expense of more useful things. In most actual combat situations, all it will do is let you die last.

[Mirikon]

I agree with Umaro. Full defense is nice for when the uber-attack of DOOOOOOOOOM is heading your way, but most of the time it is better to take the increased chance of being hit, and still be able to shoot your enemy in the face. Kill them first, and they can't try to kill you any more.

[Glyph]

Full defense can be very good when used judiciously.  Against enemies who are as lethal as you are, it can be the difference between getting hit by that full-auto burst, and narrowly dodging it.  Against mooks, it is often worth it as an interrupt action, because mooks typically don't have the multiple initiative passes that you do.  Take your action, then take full defense as an interrupt action and let them use up their attacks, then use your last action to attack again (assuming a 3 IP character).  Shadowrun characters tend to be eggshells with hammers, so shoring up the "eggshell" end is worth it.

A good, basic combo for defense is move-by-wire: 2 (with the Restricted Gear quality), reakt, and a dodge of 4 (raised to 6 by the move-by-wire) with a specialization in ranged.  That gives you (assuming a base Reaction of 5) a passive defense pool of 11, going up to 17 for full ranged defense.

[Makki]

since the OP didn't destinguish betweeen ranged and melee, I'll throw in a little reminder, that in melee, you can be on constant full defense, when using the Two-Weapon-Fighting maneuver with two small melee weapons.