[experiment 626]

i suggest with your hq's that you avoid trying to out-assault a chaos foe because they simply do it so much better than you can!
- a cheap, 2 wound chaplain can make a good leader and is great for leading a counter-assault due to his 'litanies of hate' special rule!
- an epistolary with feer of the darkness and fury of the ancients is killer against any non-cult chaos army! his main downside being, he's very expensive pts-wise and still can't quite cut it in assaults as compared to his chaos lord opposite...
- a commander is generally not that great because he's the worst assaulty character space marines can have... use only if you think you really need an entire Ld10 army, and keep his equipment to a bare minimum.

how are you scouts armed? if they've got bolt pistols & ccw's, then i recomend getting another box and making a full unit of 10 led by a vet sergeant with power fist, melta bombs & teleport homer. (the homer is only needed if you plan to deep strike your termies, otherwise the fist and bombs is fine!)
scouts are the the ultiment assault unit in a space marine army - cheap, lots of attacks and fast through the use of infiltrate and move through cover!

for your tactical squad/s, you'll want plasma guns... granted it's obvious and everyone does it, but having ap2 rapid fire guns against other power armoured foes really does help!
flamers can be a neat little surprise though too, and are more usefull if you face lots of daemons as they generally lack high armour/invulnerable saves! (the plasma gun would be ineffective orver-kill in this case!)
the main thing to avoid in tactical squads is over generalising... specialise a bit and you'll find your squads are much more effective! (for example, don't mix a long ranged, anti-tank lascannon with a short ranged, anti-hoard flamer!)

land raiders are huge point-sinks in anything below 2000pts games... a predator with 3 lascannons or a devastator squad with 4 rocket launchers is much better and costs far fewer pts!

hope this helps!
cheers!