I like this thread. In the last i guess two years I've probably play 100 games with my guard with all sorts of different builds. I'm luck in that I happen to own some 30 different tanks and roughly 300 Infantry so I can field just about anything at this point.
Thoughts on units I've used a lot:
CCS - The review is pretty dead on. You use them as assault weapon or as fire support. I would like to throw out a 3 use. Bodyguard. If you use straken, his abilities are so important to the build that you really should put stealth on the squad and take the medic and body guards. He's that good in a foot force with a strong
hth element. The other thing that should be mentioned is that if you run the assault weapon squad that they can give themselves bring it down with turns them into the best hunting tank unit in the game. I ofter stick them in a vendetta, espceially against an army with a landraider. Finally, when I run them on foot I take them simply with a hvy weapon and a vox an somethings cammo cloaks. It's nice to go to ground for a 2+ then have a second
CCS to use get back ont he fight on them. It's cheap and annoying enough that my opponent quickly targets something else. Finally the astro path is pretty much mandatory in mech guard and especially potent if you run
El al rajrahim.
Straken - You basically run him in a super resilient
CCS and combine him with 2 big blob squad with commissars, lascannons, melta bombs and power weapons. You shoot the first two turns or so then charge the objective. These blob squads will totally shock you how strong they are. I regularly chew through things like thunder wolf cav and
TH/
SS termies. Just beware of the flamey psychic power of the
GKs.
El al rajrahim - (sp?)

Anyway, the "like the wind" order is really sneaky it can really catch people by surprise. I used to use him with my SOB immolator army... Now I use him in my foot guard army. He comes in with a squad with melta and a 30 man blob squad with meltas and commissar power weapon. Remember his special weapon, but more importantly remeber his plasma pistol!
Marbo - I pretty much get his points back every game. The trick is to not let him bite off more than he can chew. He has some amazing uses though. I regularly tie up units like rifle men dread with him. Also don;t forget to use his sniper pistol, and that he has melta bombs so you can harass and sort of artillery vehicle and finally he has stealth so he is usually 2+ in cover. don;t be afraid to go to ground and let your opponent waste fire on him.
PCS - max flamers... sometimes they just win you a game.
Infantry squads - So usually I just run then with an auto cannon in a chimera with a heavy flamer. solid amount of fire power. The other way I run them is 4 strong with 4 lancannons, commissar with power weapon, vox, powe weapons on the sgts and melta bombs. These big squads do a surprising amount of damage with first rank fire second rank fire, and bring it down with the lascannons i really powerful. Especially when you can pretty much ensure they will fire alll game long... With straken the go simultaneous with marines. Seriously though these guys are the best thing in the codex. At something like 'ard boyz if you could field it you would probably win if you took all chimeras with meltas and autcannons and hvy flamer on the front. It's just unkillabe at some point and puts out tons of damage.
hvy weapon squads - 3 auto cannons. I really like this unit. I always end of taking a couple of them and putting them out in the corners. Then tend to do well as transport openners and if peopel are shooting them they are wasting their time. Their leadership sucks though. Which is fine unless you plan on taking a ton of them. Then it's actually useful to take a lord commissar... but I'm talking a tons of them... Their
LD sucks so ignore using orders on them.
special weapon squads - so these have been slowly replacing my use of vets... I like the special weapon squads inside vendettas. cheap enough not to care if the vendetta goes down but you can never ignore 3 meltas...
penal squad - so most people miss why these are good. They are cheap, they are harmless and the can outflank. In larger games an 80 point outflanking unit the hides somewhere can be awesome at big tournies like adepticon. They score and can do this like get those objectives like a scoring unit your opponents deployment zone, or holding table quarters. And because the basically can;t do anything it's easy to be disciplined about their use
Vendettas - lacannons and hvy bolters, just fill soooooooo many holes in most
IG armies. I used to out flank them, now I usually start them ont he board and just use them like gun platforms. Long range is your friend and beware of out flankers with melta guns...
Hydras - A lot of people don;t get hydras, but if you cost it out. they are poitn for point the bast transport unit you have. The other overlooked item is the strength of squadrons and how the rule work. If you use two you can pretty much use one to give half the unit hull down and point the front one at the most likely target givign you 4+ saves... Also two cost the same as a vendetta or an
IG squad in a chimeras, or a menticore, etc so it causes target confusing with everything costing the same amounts.
Manticore- These are hit or miss, but usually awesome because of the strength 10. They pretty much always have a target, and you roll each template separately, so they are pretty accurate. Also the S10 is great for obliting things like thunder wolf cav and units that have
FNP. So consider them in armies that have those rules. I can't tell you how many times I've swatted characters hiding unit because of direct S10 hits.
Psychers - So these guys get a bad wrap but I consider them mandatory. I take two units of 8 usually. The range is important to know as you can usually skirt on the edges of psychic hood for the first couple turns. This is when they shine. forcing leadership testing at -8 when units are on board edges can be incredibly useful for running things like thunder wolf cav off the table turn one. Keep them deployed towards the edge of you formation so you can skirt that 24" zone as long as possible. When you play fearless armies you usually just sling pie plates which are reliable enough to make opponents fear them. Also consider using marbo as a fear point. You cause a unit to run and they end up within 6" of marbo they can't regroup, even with
ATSKNF!!!!
Creed & chem cannons - really fun occationally. I run two chem cannons and hell hound. really you will find you can only get two tanks in and the hell hound shoots over the top.
Devil dogs - surprizingly useful if taken in large amounts, but it radically changes the standard composition of you army. All of a sudden you want to run things like eradiators and 9 hydras to make up for the loss of vedettas and the over compensation on the niche that manticores usually sit in.
Medusas - really liked these at first but they just don't do as well as manticores...
Basalsiks - I still field these occationally. I run 2 with a griffon. I think people forget how good they are and the griffon makes them deadly accurate. I like this unit at higher poitn costs where a manticore starts falling behind in fire power compared to the rest of the army.
Ves - God I love meltas and demolitions, but the damn things are expensive and I find I replace them more often then not now a days for more bodies.
Sentinals - Largely overlooked, but if you want to maximize your alpha strike, these guys with hunter killer missile are truly your best option. Build specific though.
Demolishers - I really wanted these to work. And trust me they do. The trick is the plasma cannon sponsons, tehn toss in 2 lemans and this unit is just freightening to behold. But it's expensive and needs to be bubble wrapped to stay alive!
The rest of the codex I've fooled around with but just tend to ignore at this point. I've tried a lot of different builds but haven;t been able to win constantly with other stuff. The other thing that should be noted is the loss of
DH inquisitors. It made
IG very vulnerable in some ways....