I think BA tac squads may even be the most versatile unit in all of 40k. I often take a tac squad with a veteran sergeant with power weapon, and I throw in a flamer and a missle launcher - I mount the whole unit in a rhino... now this unit's primary purpose is to land supporting assaults - they do it like this...

Drive up to enemy - dismount, vet serg and flamer at front - flamer fires (careful to leave at least one mini within 6 inches of our unit (don't want to deny ourselves the assault now do we!), usually the rest of the squad actually holds fire (for fear of wiping out the entire squad - or more likely just removing enough models to deny us the charge!). So the assault phase comes - this is why we've given the vet serg a power weapon - with our charing bonuses he can often take two or three people down, then the rest of the squad may drop another two or three - this can wipe an enemy unit entirely (giving us a sweeping advance) or else it really puts a dent in the enemy unit.  Now keep in mind this is a supporting assault - which means I have another capable BA Assault unit adjacent (I may even have two such units nearby), and the rest of my army is firing on the adjacent unengaged enemy units (the art of the coordinated assault!). This may not work as well with non-Blood Angel units - but is great for Blood Angels.

 The missile launcher is taken because of lessons I've learned the hard way, rhinos blow up, they blow up often and sometimes for no good reason... depending on where your rhino is WHEN it blows up the mission of your tac squad might suddenly change to fire support - the bolters you have help this, but the missile launcher is what really gives the unit firepower. IF your rhino happens to pop near the enemy line you can still have the unit walk forward to get into a nice "second wave" kind of assault - or if they are too far away they become a dedicated sit and shoot unit supporting your other assault units.

If going against an armor heavy foe I often swap out the flamers for a meltagun - it's an assault weapon so I can drive up, shoot at any nearby armor - then assault a different unit. Now keeping in mind that there are other assault units nearby (also likely with meltaguns and probably a few plasma pistols too) this can be quite interesting to enemy vehicles near the point of contact :-)

Dismounted tac squads - fun for more defensive operations when you just want a tad more firepower (while being able to absorb damage too) try a 7 man tac squad with two heavy weapons (the heavy weapons are what you're banking on - the others are just bodies to take hits to save your heavy weapons). If I weren't a BA player I might be tempted to take a 5 man squad - but honestly I like being able to take a few hits... and in a BA army you have to have enough people to afford possible losses to the Death Company hence (in my expereince) 7 is about the minimum you want to go with in any unit. I occassionally take 6 because I dropped a man to buy some fancy gizmo that I felt was crucial - but I consider that unit understrength from the getgo.

I love my Blood Angel tac squads :-)

~ Brother Edward