Recently, a poster in the QS forums asked about the 'seasons' of Magic. This is short-hand among Magic players for talking about when a particular format is in vogue, stemming from the way Pro Tour Qualifiers (PTQs) are organized. For example, the next Pro Tour is PT Gatecrash in Montreal, Feb 15th to 17th. The current qualifiers are Return to Ravnica (RtR) Sealed Deck with top eight booster draft, winner takes the invite. So the current season would be called "Limited Season" and it runs into December.
Limited season is of little interest to the MTGO speculator, as any bump in supply from PTQs will be a drop in the bucket compared to how limited play normally impacts the market. The 24/7 drafting that occurs online overwhelms the supply injected by PTQs, so don't waste any time thinking about how limited season affects prices on MTGO.
Going slightly out of order, the final season of the year is Standard, running from the spring to the early summer. Constructed seasons are generally good for speculation in the world of MTG finance, but MTGO is a different beast and I have never found it profitable to speculate on the Standard season.
Standard is the dominant constructed format online. It attracts more players and fires more tournaments than any other format. Any additional interest in Standard during the season will simply be drowned out by the ongoing, sustained level of interest it always enjoys. In other words, the player base is already invested in Standard, so there is no premium to be gained due to Standard season. Price fluctuations will merely be a result of shifts in the metagame. This translates to little extra benefit from stocking up on Standard staples prior to the season.
The winter Modern season is the important one for MTGO speculators. The next round of PTQs feeding PT Dragon's Maze, will be Modern Constructed. It follows that during the period of January through April there will be extra demand for Modern staples as players practice and compete for PT invites. The resulting in-season premium is the main reason it is worthwhile to speculate on Modern staples, especially the out-of-print ones.
Mid-season shifts in the metagame also drive prices as strategies come in and out of favor. A staple that doesn't see a price bump at the season's outset could very well end up spiking later as the metagame develops. There are usually a few cards that see price gains later in the season, and Gatecrash is bound to impact the Modern metagame.
Modern, unlike Standard, sees fluctuating interest. These fluctuations drive prices up and down, giving speculators the opportunity to buy low and sell high. It's good to be aware of the way interest in different formats is driven, but for the MTGO speculator, the most important season is Modern as it offers the best speculative opportunities.
Here are a few cards worth buying in the coming weeks with an eye to selling during Modern season. All prices from MTGOtraders.com and current as of October 31st, 2012.
Karn Liberated (12.93 tix): This mythic rare recently rotated out of Standard and appears as a four-of in R/G Tron. Although that deck didn't make much of a splash at PT RtR, I expect it to be played in greater numbers online. It beats Affinity and other non-interactive aggro decks quite handily, and those decks are typically over-represented online relative to IRL. Karn is also a 3rd set mythic and has found a price floor of 12-13 tix. It could see a price closer to 20 tix mid-season. Further, people love RG Tron - it's cheap to build and the dream scenario is really fun.
Grove of the Burnwillows (7.74 tix): Another four-of from R/G Tron, this is again a 3rd set rare that will see higher in-season prices. Expect it to reach 10+ tix.
Vendilion Clique (23.41) and Tarmogoyf (53.22 tix): Both of these saw a recent fall in price due to the announcement of the Modern Masters set. Both will still be pillars of the Modern format in January, so be sure to load up on these in the near term if you've got the tix. In-season prices of 30 and 70 tix respectively is not unreasonable, with higher prices possible. Remember that Modern Masters comes out after the PTQ season, so these cards will not be affected by reprints during peak play.
Creeping Tar Pit (0.83 tix): This U/B manland might not produce the best combination of colours for the current Modern format, but the Dimir guild (and the rest of Gatecrash) will arrive mid-season with lots of new multicoloured goodies to shake things up. This card saw peak prices over 3 tix last year and is an easy buy right now.
Cryptic Command (8.78) and Gifts Ungiven (4.57 tix): These two blue instants have seen quite a bit of play in the format. They are also from older sets and in-season prices have peaked at 15 tix and 13 tix. Real estate is often the best investment in Magic, but blue instants are not far behind.
Damping Matrix (0.12 tix): Modern sideboards sometimes cry out for this card's effect, and so for the speculator on a budget this is a cheap one to buy into at the current price of 0.12 tix. This occasionally went for 1.5 tix last year mid-season, and hails from the original Mirrodin, a set with a relatively low print run.
Breeding Pool (13.58 tix): It produces blue mana, is another 3rd set rare and it saw play in the BUG poison builds, which will be a good alternate deck choice for aggro players if Affinity gets hated out. This one should get to 20 tix, but don't get caught holding these after Gatecrash is released.
There are lots of other cards I expect to see play in Modern, but due to current high prices they are hard to recommend as buys. Scalding Tarn is one of the most used fetch lands in the format, but at close to 9 tix it's already well above in-season prices from last year. Twilight Mire is likewise a must-play in current Jund builds and quite a scarce card. It's also carrying an in-season price. Godless Shrine and Stomping Ground are both close to being good buys; 1 to 2 tix cheaper and they'd be on my list of recommendations.