The general thought on class combos goes something along the lines of:
I personally lean towards a soldier->consular as my prefered class for being adaptable and well-rounded, but anyway here's an interesting melee combo that some of you have surely come across and which I recommend for the "Holy ****!" factor:
Scndrl7/guard13 is probably the best way to do it.
The idea is to sacrifice the combat diversity of a soldier/guardian combo for the massive damage potential resulting from the scoundrel's sneak attacks. You give up a number of feats by choosing the scoundrel so you pigeon-hole yourself into one type of combat...specifically dual sabers or a double-bladed saber with one line of combat feat (flurry, criticals, or power attack). You also give up a good deal of HP while you're a scoundrel. On the other side, the scoundrel makes up for this some with Scoundrel's Luck. A scoundrel 7 gets a +4 to defense, which comes in handy for melee builds. And as long as you don't get carried away with scoundrel levels, you only sacrifice 2 in attack bonus compared to a soldier/guardian.
Where this build shines is taking advantage of the fact that any attack against a stunned/immobilized/incapacitated opponent counts as a sneak attack. Several Jedi powers have this affect including the Stasis line (for LSers), the Insanity line (for DSers), and the stun effects from Force Wave. In addition, all attacks from a Force Jump count as sneak attacks. With Master Speed and dual sabers or a double-bladed saber you get four attacks, each counting as a sneak attack whenever you Force Jump or whenever you attack a stunned opponent. A level-7 scoundrel gets Sneak Attack IV, for 4d6 or 4-24 sneak attack damage per attack. At four attacks per round that's 16d6 extra damage, or 16-96 of sneak attack damage per round if you score on all four hits...an *average* of 56 damage per round due to sneak attacks!
To be sure, the extra damage is more than you need in most cases but it does have it's uses in certain cases and it can be fun to watch massive damage numbers flying across your screen.