I want a good metal/hard rock amp with high gain for practice and jam sessions, maybe up to 30 W but not more. If it has built is effects, that's good but its not really a necessity for me. I heard tube amps are good. If I can get one inside my budget, that would be great. I can spend around $500. What's the best I can get?

I'll also be getting a ESP M-II or a high end Dean. So recommend amps that would go with that guitar.

Well, I'm generally not a fan of solid state amps, but if you want 30 watts or under and lots of gain and distortion that's probably your best bet for under $500.
Check out the Roland CubeX 30 or a Vox Valvertonix. There is also Line 6 Spider. Most guys who are serious about good tone hate the Line 6, but I guess the amp does have some usable presets if you want Metal sounds.
Anyway, check out the 3 of those, but again, for your budget you are going to either get a low end tube amp or a higher end solid state. Another option is to get a used tube amp, but generally the lowest wattage you'll get on those is 50 and 50 tube watts is LOUD!

i think the vox valvetronics is probs the best bet it sounded the best out of the bunch .....i did however buy the spiderjam line 6 for its backing jams etc i found it to be great for practicing , i would never use it live as i have a top notch valve head ... if i was buying the amp on pure sound the vox is the better one , they do the xxl range also and may suit rock styles slightly better but both are good .
my choice of practice amp
1 spider ( valve) 1x12
2 vox valvetronics or xxl range
3 maybe the new peavey viper range ( i have not tried but heard it is good ) or roland cube
4line 6 spider
all have fx built in ..

What about an Laney LC30 tube amp? Peavey Windsor Studio is another option. Egnator have a new 20 watt head that looks brilliant too, I think you may be able to get that and a 12inch speaker cabinet somewhere around your budget.

I don't know if its a high gain amp. But Carvin has a 2x12 practice amp. Now its 100watts which i know your not looking for something with that much power. But needless to say its a 100watt practice amp that you'll spend something like $350. And its a solid state amp...so probably not striking your interest. But Carvin has a very good sound for a GREAT price

Get a Peavey Valveking. All tube, lots of gain and only $420.

Yeah the Valveking is great. I don't have one but a buddy does and it sounds great.

I would go for the Peavey VYPYRs...

I think the 30watt model is only $199 in the US - it comes with 12 amp models, each with clean and OD channels, built in effects (both stompbox before the amp models and rack effects after the pre-gain), has a line-out for direct recording, an aux-in for playing to your favourite backing tracks etc. ...

While it is not a tube-amp, it does sound decent on its own and also has a certain tube-like feel to it (at least better than the Behringer- and Line6 modellers I've tried). That's probably because the amp models are analog, based on their Transtube tech - not pure digital (think Tech21 and their Sansamp).

Although all of the amp models are more than usable, the Peavey models alone are worth the price (JSX, 6505/5150, XXX). The 6505 is veeeeery close to the real one, and also at low volumes! I guess if you're going for high-gain you will be more than happy (the Rectifier model is not so good unfortunately...).

It's great for bedroom volume practising, but can get pretty loud...
Hope that helps!