link diversity is very important
heres just a couple of link types for my very small 2cents
web directories (put them all on tier 1)
high pr article sites
high pr wikis
multi user blog platforms
press release
there are many many more, but i thought id let someone else have their 2cents,
but get a spreadsheet, and put the levels/tiers you want/need - fill it out with each domain/site you want to do
you can get free spreadshhet software at openoffice.org if you dont have excell - its just as good and free.
do a spreadsheet for each domain, as each one will have diiferent types of links, you can add to/adjust the tier as you go on. etc
if you are targeting yahoo/bingywingy only then you can rely on much lower quality links.
also much more competitive terms will need bigger/more complex linking structures.