Some consider protein powder a supplement, some don't. Its a matter of semantics. I don't feel the need classify it. That being said, the only other supplements I use in the off-season are those which are geared towards management of common deficiencies/general health, pre and post workout "nutrition" and stimulants.
Multi Vitamin Multi Min to include @ least: 1 gm C, 400IU E (d as opposed to dl when possible), 15-25,000IU beta carotene, 200mcg selenium, 1 gm calcium, 500mg magnesium (or take ZMA), B50 complex.
Joint Support: 1500-3000mg Glucosamine, 1200-2400mg chondroitin, 1-3 gms MSM.
Omega 3's: @ least 3 gms/day. That's 10 x 180/120 gels.
Pre-Post Workout: I use what Milos calls the "Fed Ex" system. 5-10 gms creatine, 5-10 gms glutamine (preferably peptides), 50-150gms dextrose/50-75 gms whey. Vitagro is probably best if you are not averse to paying $8/# for a carb. I can't bring myself to do it personally. Sometimes I like to add BCAAs, if budget permits. I add taurine @ 5-10 gms post as well. I actually prefer Gatorade pre during the off season.
ZMA: most multi vit/min will be lacking in magnesium and even if they are not calcium and mag compete for absorption, so I opt for ZMA qhs. Its cheap and helps some people with regard to sleep patterns. Melatonin @ 1-3mg can be added here as well.
Ephedrine HCL & Caffeine 50mg/200mg 2-3 x per day. Pre workout I usually take 100/400.
There are many variations within this cost wise of course. More concentrated fish oil for example, quality of proteins, type of creatine, etc, etc. There are also other considerations to specific situations, like Slo-Niacin if ldl/hdl ratios are an issue and if you are not using 17aa orals, in which case you want to explore regular niacin. But this is a good basic guideline for off season supplementation & general health. It is up to you and your pocketbook if you want to exceed the mins and evaluate if you are able to achieve greater efficacy.
Rex.