Although many of the standard LOGIC PRO Plug-Ins are good tools there are specialists which definitely  bring the DAW to another level.
My favourite Plug-In EQs are the Neve EQs from the UAD (especially the 1081 for its flexibility AND sound), the Waves SSL Channelstrip EQ (very flexible and with really tight sound - ideal for everything that needs to be EQd a bit more but still be upfront ) and the URS Channelstrip Pro (although its very high flexibility often is too much - but it still sounds nice and clean). The TriTone Hydratone EQ is an analog, fat sounding EQ with the benefit of its own type of “saturation” which often can substitute a compressor. For extreme clean EQ i sometimes use the PSP Neon HR and for some different character i also have the Waves API EQs (wonderful sound, cool to improve a source, but definetly hard to use if there are problems in the mix)
My favourite Plug-In Compressors include many of the UAD cards: LA2A (for densitsy), Neve 33609 (for tight punch and “glue”), 1176 for snap and aggression (of course i still prefer my hardware clone - but hardware is another post), PSP Vintage Warmer 2 and Mixpressor (for upfront, hard sounds - fat, but often to intransparent for acoustic sources). The PSP Master Comp is a good sounding transparent one (and can be mixed in which is always a benefit) but is so hard to the CPU (or programmed badly) that i try to avoid it in a dense arrangement and if i dont bounce.
Before someone asks… if you only can afford ONE EQ/Compressor plug-in you should get the URS Channelstrip Pro - its affordable and you could mix quite anything with it. If you have a higher Budget get one or better two UAD cards with at least the following Plugs: 1176, LA2A, Neve 1081, Pultec Pro. Get the Waves SSL Bundle or the URS Channelstrip Pro on top and you really have a good bandwidth of sounds to mix with.
Reverb and Delay… Yes, i heard about people using those… One of the best tips i can give anyone: Get an Impulse Respone Reverb (LOGIC Pro comes with the Space Designer for example) add good Impulses and get creative. For fast tracks try to shorten the standard Halls and Rooms so that they only give you the early reflections (you get depth and the feel of space but not the muddy wash of long reverb). Space Designer has a great envelope for shortening - try it (if you own LOGIC that is). For acoustic or orchestral Sounds use Waves IR-1, IR-L or Altiverb. They do sound a bit more realistic.
For Chorus, Flanger, Phaser i really like to use the UADs Roland Chorus and Dimension D, PSP Nitro and the collection of Audio Damage. A Budget tip - they are really cheap ($29 to $49). Go figure:Â www.audiodamage.com