Well, I'll add another Spycraft reccommendation (gee, wonder why).
I can tell you right now that the game isn't going anywhere. The fanbase is strong enough and the game is solid enough. Besides, if your mentality is "oh, everyone else is buying d20 Modern so I'd better not buy Spycraft" then you will miss out on a great game. Don't getta me wrongo, I love d20 Modern too. But they're for two different types of games. Besides, Spycraft has ten times more first-party support and a couple of third-party supporters too, so it's going to have plenty of product.
Also, I've heard some rumblings from some of the d20 publishers that they're "waiting to see" about d20 Modern before supporting it. Wuthout key first party support, I'm not certain d20 Modern is a more reliable line than Spycraft.