I hate to be the one to tell you, but IM are basicly the best psytrance out there that I've found in years of searching. There's plenty of other stuff, some of it very cool, but I've not found anything that tops the mushroom yet. Still, they've got a ridiculous ammount of music out so chances are you should get at least a few months of nothing but them before you get bored.
Aphex Twin is great music, but it's a completely different genre from PsyTrance. Aphex is Intelligent Dance Music (IDM), with roots in DnB and Ambient. Like I say, great tunes, but fairly unrelated to psy. edit: That's not to say Cathodical shouldn't check out Aphex Twin btw, he should. And just to make one of my posts at least slightly positive, there's a group called "Xenomorph" who do some Psy, it's fairly metal influened at times but mostly it's solid music. And for any of you poor people who havn't already come across it: Ishkur's Guide To Electronic Music is a fantastic way of finding new tunes similar to the stuff you already like and discovering plenty of stuff you didn't know existed.. Don't take his genre definitions and descriptions as gospel, even he says he's biased as hell. But broadly his definitions are right imo. edit2: Damn that site takes over my playlists. Out goes the relaxing piano tunes, in comes Black Sun Empire!
I am a huge fan of Astral Projection, which I personally think is better than Infected Mushroom but of course it's all a matter of taste If I were you, i'd give it a shot. Astral's got some great hit songs that you will most likely enjoy
Ill just whip out some names then. Bizarre Contact, Broken Toy, GMS (Growling Mad Scientists) are awesome too.
My dosage of goa and psytrance these days has been courtesy of Astral Projection. Their older material tends to be better, namely the track Life on Mars. Juno Reactor's older material may be similar to what you like, but if it's the contemporary goa movement you are digging, then try other names.
Here is a list of a few artists to check out that are all psy/goa, aphex twin is more IDM than psy or goa. Eskimo Skazi GMS 1200 Mics Alien Project Astral Projection Astrix 2 Minds Cosma Cosmo Tech Dali exaile Hydrophonic Infected Mushroom Space Cat Yahel XSI Audio-X Audio Brains Narcophone Psysex PsyNina Rinkadink Dark Soho Atom Green Ohms Dynamic