Nothing really interesting on PS2 until the end of August, then there are a ton of good games coming out including Scarface, Splinter Cell: Double Agent, Rogue Galaxy, Disgaea 2, Valkyrie Profile 2. Final Fantasy 12 and Xenosaga Episode 3 both out in the later fall.
Gamecube has nothing that PS2 won't be getting. Only Baten Kaitos 2 (if it even makes it here), Twilight Princess, Splinter Cell: Double Agent, and Kirby Adventure look interesting this year.
PC: Spore and Civ 4 expansion out this fall; I don't really follow PC too closely.
DS: Has a lot of games: Big Brain Academy and Magnetica are both cheap purchases coming out next week. If you like Harvest Moon, that is also out next week. Later on in the summer are Starfox Command and Contact (RPG) which both look really good; also new Megaman ZX (which actually looks good, and I'm not a Megaman fan like Eric and Don for example). For Epic Adventures and RPGs out this year that you might find interesting (correct me if you like Pokemon games =P):
Legend of Zelda: The Phantom Hourglass
Tales of the Tempest
Xenogears Episode 1 and 2,
Children of Mana
Legend of Arcadia
Dark Reflections
Rune Factory: New Harvest Moon
ASH
Azure Dreams
Final Fantasy III
Open Season (A survival Adventure game by Ubisoft)
Eragon
Shin Megami Tensei
Dragon Quest Monsters
Baten Kaitos
Lunar Knights (The word "Lunar" is not meant to be a reference to the series Lunar)
Some strategy simulation titles: Panzer Tactics, Black and White, Dynasty Warriors. Some other interesting titles, like Hotel Dusk Room 215 (which I am definately buying). Not a lot this summer, but during the fall there will be much more than can be handled =)
More hours of gameplay than there are hours in the last few months of the year =)
So yeah: Only DS has anything that I find particularly interesting until the end of August. There are also games already out for DS which were released in the past few months that I have found are really good.
-Insert Inspiring Quote-