Spend your money on a good convolution reverb (e.g. Altiverb, LiquidSonics Reverberate, others. Though the reverb plug-in is not as important as the impulses that you get, esp. in Altiverb). Secondly, AudioEase Speakerphone and iZotope RX are significantly useful products.
In terms of EQs and compressors and a bunch of other stuff, not that necessary. You can use the stock stuff that comes with your DAW, or download freeware plug-ins (especially useful for basic effects plug-ins).
Once you can afford them, you might want to look at the GRM Tools package (for which there are some variable alternatives, from Elevayta and Michael Norris for example, or NI Reaktor, MeldaProduction as well). These are effects plug-ins though. Loads of freeware VSTs in this department as well.
Mostly I would suggest looking more at sound effects packages, rather than plug-ins, because those are tremendously more useful. Online sound effects sites like SoundDogs are great, because you only pay for what you want. Or (better) recording gear, mainly microphones.