Creatine Monohydrate, 5g - Increase lean mass & strength, improve muscular recovery
Fish oil (300mg EPA & DHA per capsule), 8-10 caps - Reduce systemic inflammation, improve recovery
Fiber tablets with ChromeMate (2g fiber per tablet), 3 tablets - Keep me regular
Vitamin D (2000 IU per pill), 3 capsules - As an office worker I don't see the sun much. This helps take care of that deficiency.
Acidophilus probiotic (1,000,000 organisms per caplet), 3 caplets - Improve digestion and gut health, allow me to absorb all my nutrients effectively.
Whey protein concentrate - I use it when I'm low on protein for the day, otherwise not a daily supplement.
Magnesium, 400mg - Improve sleep and help regulate anabolic hormones.
If I had to choose a couple which were most important, I would choose fish oil and vitamin D, as they seem to have the best benefit profiles. I'm considering some others such as Alpha-Linoleic Acid and EGCG, but as of now I haven't pulled the trigger on them. You'll also notice I don't take a multi-vitamin. From the research I've seen, and the quality of food (and quantity of vegetable matter) I consume, I don't find any compelling reason to take a daily multi. The only vitamin I'm ever low on is D, so I supplement that on its own, but everything else is fulfilled solely by food.