first of all, I have to use pixel art, vector's are not detailed enough for my taste

Eh? Vectors are as detailed as you make them.

1- If you make detailed vectors wouldn't be a PITA to render it? Even a vector editor like inkscape takes minutes to render a moderately detailed vector image.
I can't imagine what it could be like to load tons of game objects, maps etc...

2- And still I don't think you can achieve the same detail level. In raster you can simply push pixels. There is no limit. Think of a classic hidden object game screen. Like this one for example: http://games.bigfishgames.com/en_polly-pride-pet-detective/screen1.jpg
And here is a screen of WoG which I think is entirely done in vectors: http://www.co-optimus.com/images/upload/image/world-of-goo.jpg

I know these are not the only examples and there could be more detailed vector games but it has surely a limit. And that limit is way low for my taste

Anyway let's not make it a vector vs raster flaming. this is just my personal idea.

thanks for the replys guys.

first of all, I have to use pixel art, vector's are not detailed enough for my taste
I also don't worry about GUI for now since the game I'm planning to start, won't need any GUI other than menu and some labels.

I played aquaria's demo and I remember it being blurry when the camera zoomed in to the main character. It wasn't that bad actually.
So far, producing the textures according to the highest resolution (thanks lithander and eclipse) and scaling down with a nice filtering seems to be the best choice.

Still there is no solution for widescreen resolutions though. If one wants to support 4:3 and Widescreen, viewport can't stay the same. I will need to show more of the level (as stated by Will Vale) and that bugs me a lot since it would affect the game play (regardless the genre).

EDIT:
Here is the list of aspect ratios that I want to support

*5:4 (17" LCDs)
*4:3
*16:10 PC Widescreen
*16:9 TV Widescreen (for consoles with HDMI support)

are there any 2D games that support all these ratios? I would like to observe and analyze it.

ah ok, so in OpenGL I can scale a quad once and not worry about it later?
i'm still thinking SDL way so sorry if I sound stupid 

also: why would you have to scale in every game loop?

what I thought was something like this,

1- draw every object to a buffer screen in size of 1024x768 regardless the resolution
2- scale it to the actual resolution
3- draw the buffer to the screen

so every game loop has the step 2 for extra.

hello guys,

what's he best method of having an independent viewport in 2D games regardless the resolution?

first thing that came to my mind is to make the game for the most used resolution (1024x768) and scale the texture down or up right before drawing to the screen.

downside is, it still can't handle different aspect ratios (i.e: widescreen), scaling in every game loop can affect the performance and there may have glitches because of the scaling.

so what do you, experienced game designers, have to recommend on this issue?

thanks