nijo was cool...
the kyoto temples are all the same..with i guess the exception of kinkakuji - which is gold plated...
if youre in kansai, you should make a stop at nara which has a ton of deer just chilling on the street..also, if you have time, hit kobe for the best beef youll ever taste in your life (my recommendation is a place called wakoku (和黒) basically in the same complex as the shin kobe station - which is accessible by shinkansen - my lunch was about 2500 yen [or about 20-25usd])
osaka is nice, but its hard to spend more than a few days there since there really isnt too much to do outside dotombori (a famous street in osaka with lots of stuff)...if youre really into castles, himeji is nice, its really out of the way (about 4000 yen total from osaka area), but its worth going to at least once i guess...
as for lodging in general, i highly recommend youth hostels...the best site i found for booking is here:
Hostelling International
but be aware that they typically have curfews (usually 10-11pm)..so dont expect a nightlife...if you want to roam the city at night, youre better off looking for a cheap business hotel...ive heard of prices as low as 1500/night (in diminishing quality of course...)
id write about tokyo..but i wonder if anyone will read this and i didnt read the previous replies -_-