3.5 D20 modern mash up help

[Nosta]

so one of my friends wants to start a new campaign but this time we want to try something a little different.
we'll be using gestalt rules, but unlike normal gestalt rules that info two 3.5 classes my friend wants us us to have 1 3.5 class and 1 d20 modern class.

Problem is i'm not sure what to do. I kinda wanna play some classes I never played before

on the 3.5 side I've played a soulknife a monk a dragonshaman a warmage a duskblade a scout and a ranger
on the d20 modern side I've played a strong and a tough hero before

the first thing that came to my mind was an Artificer mixed with a fast hero. but I was curious to see if the people here would have some better ideas

Advance classes and prestige classes allowed but not both at the same time
starting level 10

[noob]

Always take prcs on the dnd side.(all the advanced classes looks extremely poor)
Also T1 all the way to victory(you are already doing it)
All T1 classes do everything they want
You might try the famous
wizard 1/shadow prc 2/ incantatrix/ tons of other abusive prcs
Also with some interpretations and the right feats wizard 7 halfling whistler 1 sublime chord 1 can cast any spell at any time or prepare any spells up to level 8 and cast any spell when you want(and cast any level 9 spell for two level 8 spells)
Then you progress your sublime chordness with prcs on top of it.
You might also try planar shepherd of the far realms and other stuff of this kind.
artificier strikes as a good choice most of the time because your party will love you(Since you are going to do all the book keeping chore for finding what is a good magic item and that you will craft the perfect tools for the party).
Mostly you can do any dnd build and put one basic class from modern.(Due to how modern classes are overwhelmingly under-powered compared to dnd ones)

[T.G. Oskar]

The key on such a mash-up is to get a d20 base/advanced class that complements your D&D class, either by reinforcing its strengths or granting other features.

The d20 Modern base classes seem kinda disappointing, but they're very nice gestalt enablers. As you might have noticed, Fast Hero is a pretty solid way to get Evasion quickly (level 3, pretty much), but you should get it if you REALLY need it; the rest is mostly so-so (medium BAB, decent HP). Smart Hero works wonders with Int-specific classes (Factotum, Wizard, Wu Jen; you could add the Swashbuckler as a class as well) mostly because of the talent that lets you apply your Intelligence to attack rolls against a specific opponent (with 2 levels of Swashbuckler, you end up with Insightful Strike and Int to attack, Int + Str to damage with finessable weapons by level 3), plus you get 8 + Int skill points, a bunch of useful skills (Demolitions comes to mind; Computer Use only works if you're on PL 4 or higher, though) and the Plan talent, which is awesome for a pre-battle buff that costs nothing but a minute of preparation (it also boosts skill checks, so you can grant allies a free +3 buff to skill checks for little). Charismatic Hero has, IIRC, medium BAB and a washed-down version of the Bard's inspire courage class feature mostly for free, so it works for classes that could work as leaders but lack some of the traits (Paladins, Marshals).

Working with the restriction, you can get some...interesting builds. Any melee character could benefit from Shadow Slayer (IIRC; the one from the Core rulebook on the Shadow Chasers campaign setting), as it gets a bunch of benefits including fast healing and a version of favored enemy, as well as full BAB and a smattering of additional feats (in particular, it aids Monk a bit, and Swordsage a LOT). Thrasher does wonders on a Con-focused build, adding a Rage-like effect, Uncanny Dodge, Con to AC (at level 1) and a very nice d12 HD; pair it with something like Totemist for a sweet build. The Spellslinger from the Urban Arcana web enhancement lets you cast spells through firearms, so you could build a Wizard||Smart Hero, then overlap a bit into Gunslinger, and then get a long-range firearm and Spellslinger 5 to shoot Magical Bullets with very powerful spells (and better BAB to boot!).

In short: look for synergies between the base classes, and plan ahead. You can make pretty interesting builds just by planning ahead. My advice? Once you get the levels of Smart Hero you need, go Artificer||Scientist (an advanced class from d20 Modern); the "discoveries" work like spells, and help you pad up your utility even further, and since they're crafted much like items, you can take advantage of the item crafting feat boosters and make them faster and most importantly, cheaper.