The Toyota filter on the IS300 from the factory is 'Toyota 90915-20003'. That part number cross-references with two other Toyota part numbers '08922-02011' and '08922-02004' (according to my dealer's parts department). I just installed the '...011' on mine last night.
Since most Toyota and Lexus V6/I6 models use the '...011' number, a look in the master book at Pep Boys (or was it K-Mart) showed that this is equivalent to a ACDelco PF53 or UPF53 (for UltraGuard) and to a MobilOne M1-102.
By the way, Lexus wants to charge $9.99 for the filter and Toyota charges $5.95 for the same part number!! It must be all that loving care that the Lexus dealer uses when selling you the filter. The MobilOne only cost me $9.99. I plan on switching to synthetic at about 10K miles.
I'm no technician, just repeating what I was told by the Lexus parts dept. and what I saw in the book at the store. Don't yell at me if I'm wrong.
You can get the filter out through the top in about the only spot that you can get your arm through (right above and slightly to the rear of the filter). It was a very tight fit, but it does go through.
[RANT] WHY must every manufacturer put the oil filter in such a position that it drips all over everything when you remove it? I had a rag under it to catch some, but I still ended up with a puddle on the floor and oil all over the engine compartment under the filter. WHY WHY WHY???? The only sane filter mounts I've seen have been on a '96 Blazer and a '83 Regal. The Blazer was right up front at the botton where it didn't drip on anything else. Oh yeah, and don't spill any around the oil filler hole because you can't clean it up with the big plastic shroud around the engine. Spilling here is a little easy because the filler hole is right-angled and not very big (inside)[/RANT]