This is the chart that I use to decide what potions to make every time I rebuy my supplies. It is updated daily with GE prices:
http://runescape.wikia.com/wiki/Calculator:Herblore/Unfinished_potions
Note: The information on that page is assuming that you are making pots from (unf) potions and adding secondary ingredients. If you are doing it from scratch with herb, vial of water, secondary, there is a very similar page on RS Wiki linked from that first one.
Also, these are some potions I have made recently for cheap:
Serum 207's - Cheap to make, and they make 2x as fast as regular potions
Combat potions - Very cheap to make, about 84 xp per potion. Pots hardly resell but it doesn't matter because the cost of making them is so miniscule.
Energy potions - Just bought almost 40k of these recently. VERY slow, and only 67 xp per potion, but even cheaper than combat potions. These are the way to go if you are on a tight budget!
Spec Restore potion - For some odd reason, this potion is not included on that list of potions. These are alot more expensive (about 4.5k per potion, 23gp loss per xp) but it is TOTALLY worth it if you have some extra cash to throw around for Bonus XP Weekend! You are looking at 200xp per potion, which is 540xp per potion at the beginning of the 2.7x BXP multiplier.
I hope that helps man, good luck and happy herbin!