Gotta agree with a there PSY...
 

.....Assembly and The Deadly Tremors were awesome.
Not sure when Assembly are gigging next but I see that The Deadly Tremors are at Barfly on Jul 21st ... deffo heading to that one.

porcupine tree is awesome! check out karnivool they're kind of a mix of porcupine tree, marsvolta and tool. really good band from australia actually.

Any other great bands that sound similar to The National?

You might want to try out the Portland band The Standard. They play a pretty similar style of music, although the vocalists sound nothing alike.

Their 2008 album Swimmer was my first album from them and it does remind me quite a bit of Aligator

Awesome.

An Italian band Soviet Soviet

Soviet Soviet - Lokomotiv


The French Velvet Condom

Velvet Condom - Samt Und Stein (2011)

Bands Similar To Motion City Soundtrack/The Rentals?
 

I wasn't sure where to post this, seeing as both bands can be considered Pop Punk or Indie/Alternative, so yeah.

I'm looking for some more bands in the vein of those two, along with bands like Weezer and Anakin, basically bands that use a lot of poppy synths with big guitars and catchy hooks.

Go.

I need innovative indie albums like Hey Rosetta's Seeds.

Oh I like both of those songs ikvat posted. Pretty awesome stuff. Definantly gotta look into them

Ded Rabbit from Edinburgh are excellent. Especially they're old stuff they recorded when they were 12. Lots of saxy indie funk to be had.
Also, the Naked Strangers from Ullapool. Really fantastic live. They have a Cage the Elephant feel to them, I think they played Belladrum this weekend so they're getting some of the recognition they deserve.
Slave System, though not indie so much as alternative are also worth a listen. Sleazy basslines and fuzzbox's all round with some catchy hooks to the tune of Iggy Pop having a seizure.